diff --git a/plotly_express/_chart_types.py b/plotly_express/_chart_types.py
index fa6ce5c..a9b69d7 100644
--- a/plotly_express/_chart_types.py
+++ b/plotly_express/_chart_types.py
@@ -18,6 +18,7 @@ def scatter(
     x=None,
     y=None,
     color=None,
+    opacity=None,
     symbol=None,
     size=None,
     hover_name=None,
@@ -325,6 +326,7 @@ def scatter_3d(
     y=None,
     z=None,
     color=None,
+    opacity=None,
     symbol=None,
     size=None,
     text=None,
@@ -416,6 +418,7 @@ def scatter_ternary(
     b=None,
     c=None,
     color=None,
+    opacity=None,
     symbol=None,
     size=None,
     text=None,
@@ -483,6 +486,7 @@ def scatter_polar(
     r=None,
     theta=None,
     color=None,
+    opacity=None,
     symbol=None,
     size=None,
     hover_name=None,
@@ -774,6 +778,7 @@ def scatter_matrix(
     data_frame,
     dimensions=None,
     color=None,
+    opacity=None,
     symbol=None,
     size=None,
     category_orders={},
diff --git a/plotly_express/_core.py b/plotly_express/_core.py
index a549c57..17f9e2d 100644
--- a/plotly_express/_core.py
+++ b/plotly_express/_core.py
@@ -141,7 +141,6 @@ def make_trace_kwargs(args, trace_spec, g, mapping_labels, sizeref, color_range)
                 result["marker"]["sizemode"] = "area"
                 result["marker"]["sizeref"] = sizeref
                 mapping_labels.append(("%s=%%{%s}" % (v_label, "marker.size"), None))
-
             elif k == "trendline":
                 if v in ["ols", "lowess"] and args["x"] and args["y"] and len(g) > 1:
                     import statsmodels.api as sm
@@ -620,6 +619,8 @@ def infer_config(args, constructor, trace_patch):
         grouped_attrs.append("marker.symbol")
 
     trace_patch = trace_patch.copy()
+    if "opacity" in args:
+        trace_patch["marker"] = dict(opacity=args["opacity"])
     if "line_group" in args:
         trace_patch["mode"] = "lines" + ("+markers+text" if args["text"] else "")
     elif constructor != go.Splom and (
diff --git a/plotly_express/_doc.py b/plotly_express/_doc.py
index 30aafb2..44301e1 100644
--- a/plotly_express/_doc.py
+++ b/plotly_express/_doc.py
@@ -91,6 +91,9 @@
         "Ignored if `error_z` is `None`.",
     ],
     color=[colref, "Values from this column are used to assign color to marks."],
+    opacity=[
+        "(number, between 0 and 1) Sets the opacity for markers."
+    ],
     line_dash=[
         colref,
         "Values from this column are used to assign dash-patterns to lines.",