Abstract: A cup holder includes a fixed seat, a movable clamping bar and a support rack. When the movable clamping bar is pushed to shorten the distance between the movable clamping plate and the fixed clamping plate, the first locking teeth mesh with the second locking teeth, so that the locking block is disposed at a successively jumping state, and the rail of the baby stroller is sandwiched between the movable clamping plate and the fixed clamping plate. Then, the rotation member is rotated to drive the pull rod which drives the positioning piece to slide into the transverse slot to stop the locking block. When the rotation member is rotated successively, the movable clamping bar performs a micro-adjustment tightening action, so that the rail is clamped between the movable clamping plate and the fixed clamping plate.