Abstract: The present invention relates to a disposable safety syringe (1) including an automatically retractable needle (12) for preventing said syringe from being reused, comprising a cylindric body (82) defining, at one end thereof, a needle coupling end-piece (7) and being opened at the other end portion thereof for introducing thereinto a piston (4) having a scaling gasket (5). The feature of the invention is that on said piston are provided engaging means (23, 24) for engaging and retracting the needle (12) after the delivering of the injection liquid.