A retractable safety syringe includes a retractable needle hub holding aneedle and having afirst guiding means； and a hollow barrel having a second guiding means setcorrespondingly tothe first guiding means； and a collapsible plunger comprising of a firstplunger element having aprotrusion releasably coupled with a second plunger element having alongitudinal slot with apinched zone to curb the movement of said protrusion； and a spring disposedbetween the needlehub and hollow barrel and acts between the needle hub and the hollow barrel.The uncoupling ofthe collapsible plunger triggers the retraction mechanism to enable the needlehub to retract intothe barrel by the decompression force of a spring. The reliability ofretraction is further improvedby a longitudinal slot and a protrusion to facilitate the retreating of thecollapsible plunger in anorderly way.
