Abstract: A crank of a shock absorber for a bicycle has two ends respectively pivotally connected with a bicycle frame and a rear shock absorber, having a round hole and a disc fitted in the round hole, a rear bearing hole, a narrow groove communicating with the round hole and the rear bearing hole, a nut at one side of the groove and a bolt extending from outside through the groove to screw with the nut, the disc having an eccentric hole; a rear shock absorber has a pivot base to face the eccentric hole for a micro-adjusting rod to extend therein stably. Then the micro-adjusting rod is rotated for an angle to alter the angle of the shock absorber relative to the bicycle frame, so a user can adjust elastic force of the shock absorber according to the capability, the body weight and road conditions.