Antilock brake system for a bicycle

An antilock brake system for a bicycle is mounted to a brake mounting bracket (61) and generally comprising: brake shoe holder (20), sliding seat (30), brake shoe (40) and elastic member (50). The brake shoe holder (20) is formed with groove (22) for slidably receiving the sliding seat (30), the brake shoe (40) is disposed in the sliding seat (30), the brake shoe holder (20) is provided with an antilock slope (26), and the sliding seat (30) is correspondingly provided with a projecting slide surface (34) for abutting against the antilock slope (26); the elastic member (50) serves to retain the sliding seat (30) at an end of the brake shoe holder (20) in a rotating direction of a bicycle wheel (60) before the brake is applied.