A hub assembly for a bicycle includes a shaft (12), a hub body (40), a driven ring (43), a drive seat (10), a rotation ring (20), a plurality of pawl members (22), a plurality of push balls (23), a mounting sleeve (32), a damping ring (30), and a plurality of tension adjusting mechanisms (37). Thus, each of the pawl members is driven by each of the push balls in a rolling manner so that each of the pawl members is moved smoothly and stably without incurring sliding friction, thereby facilitating operation of the drive seat. In addition, each of the tension adjusting mechanisms is used to adjust the damping force of the damping ring, so that the damping force of the damping ring is distributed evenly.