diff --git a/CHANGELOG.md b/CHANGELOG.md
index f97d53c20da..fba36fcf691 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Unreleased
 
+- Type indent parameter in to_json
+  ([#4402](https://github.com/open-telemetry/opentelemetry-python/pull/4402))
 - Tolerates exceptions when loading resource detectors via `OTEL_EXPERIMENTAL_RESOURCE_DETECTORS`
   ([#4373](https://github.com/open-telemetry/opentelemetry-python/pull/4373))
 - opentelemetry-sdk: fix OTLP exporting of Histograms with explicit buckets advisory
diff --git a/opentelemetry-sdk/src/opentelemetry/sdk/_logs/_internal/__init__.py b/opentelemetry-sdk/src/opentelemetry/sdk/_logs/_internal/__init__.py
index d277b5cae09..1e5f57725e7 100644
--- a/opentelemetry-sdk/src/opentelemetry/sdk/_logs/_internal/__init__.py
+++ b/opentelemetry-sdk/src/opentelemetry/sdk/_logs/_internal/__init__.py
@@ -217,7 +217,7 @@ def __eq__(self, other: object) -> bool:
             return NotImplemented
         return self.__dict__ == other.__dict__
 
-    def to_json(self, indent=4) -> str:
+    def to_json(self, indent: Optional[int] = 4) -> str:
         return json.dumps(
             {
                 "body": self.body,
diff --git a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/_internal/point.py b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/_internal/point.py
index 5df32ddaae1..8c7e3469772 100644
--- a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/_internal/point.py
+++ b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/_internal/point.py
@@ -38,7 +38,7 @@ class NumberDataPoint:
     value: Union[int, float]
     exemplars: Sequence[Exemplar] = field(default_factory=list)
 
-    def to_json(self, indent=4) -> str:
+    def to_json(self, indent: Optional[int] = 4) -> str:
         return dumps(asdict(self), indent=indent)
 
 
@@ -59,7 +59,7 @@ class HistogramDataPoint:
     max: float
     exemplars: Sequence[Exemplar] = field(default_factory=list)
 
-    def to_json(self, indent=4) -> str:
+    def to_json(self, indent: Optional[int] = 4) -> str:
         return dumps(asdict(self), indent=indent)
 
 
@@ -90,7 +90,7 @@ class ExponentialHistogramDataPoint:
     max: float
     exemplars: Sequence[Exemplar] = field(default_factory=list)
 
-    def to_json(self, indent=4) -> str:
+    def to_json(self, indent: Optional[int] = 4) -> str:
         return dumps(asdict(self), indent=indent)
 
 
@@ -105,7 +105,7 @@ class ExponentialHistogram:
         "opentelemetry.sdk.metrics.export.AggregationTemporality"
     )
 
-    def to_json(self, indent=4) -> str:
+    def to_json(self, indent: Optional[int] = 4) -> str:
         return dumps(
             {
                 "data_points": [
@@ -129,7 +129,7 @@ class Sum:
     )
     is_monotonic: bool
 
-    def to_json(self, indent=4) -> str:
+    def to_json(self, indent: Optional[int] = 4) -> str:
         return dumps(
             {
                 "data_points": [
@@ -151,7 +151,7 @@ class Gauge:
 
     data_points: Sequence[NumberDataPoint]
 
-    def to_json(self, indent=4) -> str:
+    def to_json(self, indent: Optional[int] = 4) -> str:
         return dumps(
             {
                 "data_points": [
@@ -173,7 +173,7 @@ class Histogram:
         "opentelemetry.sdk.metrics.export.AggregationTemporality"
     )
 
-    def to_json(self, indent=4) -> str:
+    def to_json(self, indent: Optional[int] = 4) -> str:
         return dumps(
             {
                 "data_points": [
@@ -203,7 +203,7 @@ class Metric:
     unit: Optional[str]
     data: DataT
 
-    def to_json(self, indent=4) -> str:
+    def to_json(self, indent: Optional[int] = 4) -> str:
         return dumps(
             {
                 "name": self.name,
@@ -223,7 +223,7 @@ class ScopeMetrics:
     metrics: Sequence[Metric]
     schema_url: str
 
-    def to_json(self, indent=4) -> str:
+    def to_json(self, indent: Optional[int] = 4) -> str:
         return dumps(
             {
                 "scope": loads(self.scope.to_json(indent=indent)),
@@ -245,7 +245,7 @@ class ResourceMetrics:
     scope_metrics: Sequence[ScopeMetrics]
     schema_url: str
 
-    def to_json(self, indent=4) -> str:
+    def to_json(self, indent: Optional[int] = 4) -> str:
         return dumps(
             {
                 "resource": loads(self.resource.to_json(indent=indent)),
@@ -265,7 +265,7 @@ class MetricsData:
 
     resource_metrics: Sequence[ResourceMetrics]
 
-    def to_json(self, indent=4) -> str:
+    def to_json(self, indent: Optional[int] = 4) -> str:
         return dumps(
             {
                 "resource_metrics": [
diff --git a/opentelemetry-sdk/src/opentelemetry/sdk/resources/__init__.py b/opentelemetry-sdk/src/opentelemetry/sdk/resources/__init__.py
index fd2d1b86aeb..752b9067b77 100644
--- a/opentelemetry-sdk/src/opentelemetry/sdk/resources/__init__.py
+++ b/opentelemetry-sdk/src/opentelemetry/sdk/resources/__init__.py
@@ -297,7 +297,7 @@ def __hash__(self) -> int:
             f"{dumps(self._attributes.copy(), sort_keys=True)}|{self._schema_url}"  # type: ignore
         )
 
-    def to_json(self, indent: int = 4) -> str:
+    def to_json(self, indent: Optional[int] = 4) -> str:
         attributes: MutableMapping[str, AttributeValue] = dict(
             self._attributes
         )
diff --git a/opentelemetry-sdk/src/opentelemetry/sdk/trace/__init__.py b/opentelemetry-sdk/src/opentelemetry/sdk/trace/__init__.py
index ec5bc3f0fe5..729ceb8226b 100644
--- a/opentelemetry-sdk/src/opentelemetry/sdk/trace/__init__.py
+++ b/opentelemetry-sdk/src/opentelemetry/sdk/trace/__init__.py
@@ -483,7 +483,7 @@ def instrumentation_info(self) -> Optional[InstrumentationInfo]:
     def instrumentation_scope(self) -> Optional[InstrumentationScope]:
         return self._instrumentation_scope
 
-    def to_json(self, indent: int = 4):
+    def to_json(self, indent: Optional[int] = 4):
         parent_id = None
         if self.parent is not None:
             parent_id = f"0x{trace_api.format_span_id(self.parent.span_id)}"
diff --git a/opentelemetry-sdk/src/opentelemetry/sdk/util/instrumentation.py b/opentelemetry-sdk/src/opentelemetry/sdk/util/instrumentation.py
index a6fd7d7f66b..6b45bf2a827 100644
--- a/opentelemetry-sdk/src/opentelemetry/sdk/util/instrumentation.py
+++ b/opentelemetry-sdk/src/opentelemetry/sdk/util/instrumentation.py
@@ -153,7 +153,7 @@ def name(self) -> str:
     def attributes(self) -> Attributes:
         return self._attributes
 
-    def to_json(self, indent=4) -> str:
+    def to_json(self, indent: Optional[int] = 4) -> str:
         return dumps(
             {
                 "name": self._name,