Abstract: A crank for fitness equipment with a self-locking mechanism is provided. A crank body is provided with an installation hole, an internal thread is disposed in the installation hole, and an anti-loosening ring embedding portion is disposed at an outer end of the installation hole. An anti-loosening ring is tightly fitted to the anti-loosening ring embedding portion. A screw rod of a pedal is screwed into the installation hole of the crank body, and passes through the anti-loosening ring tightly fitted in the installation hole.