Abstract: A hub locking structure for safety syringe includes a hub-locking member that is initially located in a rear part of a hub fitted in an inner front of a barrel before the safety syringe is used to inject. In this initial position, a flange ring on the hub-locking member radially pushes the rear part of the hub outward to firmly engage an annular groove on the hub with a retaining ring on the inner wall of the barrel. When a plunger in the barrel is pushed forward to inject, the hub-locking member is moved further into the hub with the flange ring engaged with retaining holes on the hub to disengage the annular groove on the hub from the retaining ring of the barrel, and thereby allows the hub and the hub-locking member to be pulled backward by the plunger to retract a needle into the barrel.