Abstract: A safety syringe includes an injection head, a plunger and a barrel. The ection head has a needle cannula mounted to a needle seat, with the needle seat attachable to a needle seat connector. The inner side of the rear end of the needle seat connector has stoppers that correspond to protrusions on the coupling portion of the plunger. The plunger has a plunger shaft connected by a conical section to a coupling portion that has a rubber gasket. The plunger shaft can be snapped off at the conical section after use, so as to completely disable the syringe. The safety syringe has a barrel for receiving the injection head portion and the plunger such that a liquid-tight chamber is formed to hold medicine or blood. The injection head is attached to the barrel through interlocking annular edges and grooves, and remains so attached during the withdrawal of fluid and during the injection phase.