A retractable safety syringe (1) includes a retractable needle hub (4) holding a needle (40) and having a first guiding means (42), a hollow barrel (2) having a second guiding means (22) set correspondingly to the first guiding means (42), a collapsible plunger (6) comprising a first plunger element (64) having a protrusion (603) releasably coupled with a second plunger element (62) having a longitudinal slot (602) with a pinched zone (6021) to curb the movement of said protrusion (603), and a spring (8) disposed between the needle hub (4) and the hollow barrel (2) and acts between the needle hub (4) and the hollow barrel (2). The uncoupling of the collapsible plunger (6) triggers the retraction mechanism to enable the needle hub (4) to retract into the barrel (2) by a longitudinal slot (602) and a protrusion (603) to facilitate the retreating of the collapsible plunger (6) in an orderly way.
