diff --git a/gtsam/geometry/Rot3.cpp b/gtsam/geometry/Rot3.cpp
index 08213b065..6db5e1919 100644
--- a/gtsam/geometry/Rot3.cpp
+++ b/gtsam/geometry/Rot3.cpp
@@ -228,6 +228,7 @@ double Rot3::yaw(OptionalJacobian<1, 3> H) const {
 }
 
 /* ************************************************************************* */
+#ifdef GTSAM_ALLOW_DEPRECATED_SINCE_V42
 Vector Rot3::quaternion() const {
   gtsam::Quaternion q = toQuaternion();
   Vector v(4);
@@ -237,6 +238,7 @@ Vector Rot3::quaternion() const {
   v(3) = q.z();
   return v;
 }
+#endif
 
 /* ************************************************************************* */
 pair<Unit3, double> Rot3::axisAngle() const {
diff --git a/gtsam/geometry/Rot3.h b/gtsam/geometry/Rot3.h
index 18bd88b52..01ca7778c 100644
--- a/gtsam/geometry/Rot3.h
+++ b/gtsam/geometry/Rot3.h
@@ -515,11 +515,16 @@ class GTSAM_EXPORT Rot3 : public LieGroup<Rot3, 3> {
      */
     gtsam::Quaternion toQuaternion() const;
 
+#ifdef GTSAM_ALLOW_DEPRECATED_SINCE_V42
     /**
      * Converts to a generic matrix to allow for use with matlab
      * In format: w x y z
+     * @deprecated: use Rot3::toQuaternion() instead.
+     * If still using this API, remind that in the returned Vector `V`,
+     * `V.x()` denotes the actual `qw`, `V.y()` denotes 'qx', `V.z()` denotes `qy`, and `V.w()` denotes 'qz'.
      */
-    Vector quaternion() const;
+    Vector GTSAM_DEPRECATED quaternion() const;
+#endif
 
     /**
      * @brief Spherical Linear intERPolation between *this and other