In human anatomy, extensor carpi radialis brevis is a muscle in the forearm that acts to extend and abduct the wrist.

It arises from the lateral epicondyle of the humerus, by the common extensor tendon; from the radial collateral ligament of the elbow-joint; from a strong aponeurosis which covers its surface; and from the intermuscular septa between it and the adjacent muscles.

[2] The fibres end approximately at the middle of the forearm in the form of a flat tendon, which is closely connected with that of the extensor carpi radialis longus, and accompanies it to the wrist; it passes beneath the abductor pollicis longus and extensor pollicis brevis, beneath the extensor retinaculum, and inserts into the lateral dorsal surface of the base of the third metacarpal bone, with a few fibres inserting into the medial dorsal surface of the second metacarpal bone.

[2] Like all the muscles in the posterior forearm, ECR brevis is supplied by a branch of the radial nerve.

The muscle, like all extensors of the forearm, can be strengthened by exercise that resist its extension; Reverse wrist curls with dumbbells can be performed.