Abstract: A syringe with retractable needle includes a hub, a barrel, and a plunger. The hub is provided with symmetrical retaining sections, and a hooking section of a predetermined length is formed at a front end of the plunger with a piston mounted the hooking section. The piston includes a diametrically larger front part and a diametrically smaller and deformable rear part. A top surface of the piston is tightly abutted on a large lower surface of the hooking section to prevent any bubble from existing behind the hooking section. When the plunger is fully pushed forward to compress the smaller rear part of the piston, the hooking section is brought to engage with the retaining sections on the hub, so that medical liquid is fully released from the barrel, and the hub and the needle thereof can be drawn into the barrel after the injection by pulling the plunger backward.