Abstract: A safety syringe has a barrel, a needle hub movably received in the barrel and having a hollow cone with a flange formed on an inner periphery of the hollow cone and a plunger with a hook formed to correspond to the flange of the needle hub. The plunger has a spacer formed on the top face of the stop to be adapted to detachably engage with a bottom face of the hollow cone to keep the hook from engagement with the flange. The spacer is made of a material of resilience such that when the spacer is so deformed that the hook engages with the flange so as to pull the needle hub back into the barrel.