Safety syringe with retractable needle holder

The present invention relates generally to a hypodermic syringe, and more particularly to a safety structure of the hypodermic syringe. A hypodermic syringe comprises a barrel having at least one catching piece disposed at the end; an outer sleeve fitted rotatably with the barrel to turn to locate at the first position and the second position and provided at least one escape hole; a needle holder having a cylinder cooperating portion disposed slidably in the receiving hole of the barrel, a retaining circular groove disposed in the outer periphery of the needle holder for retaining the catching piece of the barrel; a plunger having a rod body capable of pulling back the needle holder. As the outer sleeve is turned to the first position, each catching piece of the barrel retains the retaining tooth of the barrel. The needle holder is unable to displace. As the outer sleeve is turned to the second position, the escape hole is corresponding to the catching piece of the barrel to eject outward. The needle holder is not confined so as to be pulled back by the plunger.