A syringe is provided. A front end of a barrel has an annular blocking portion which has at least two projections and at least two engaging slots defined by the projections, and one side of each projection has a guiding face. A connector which has at least two blocking members arranged circumferentially is assembled to the front end of the barrel, and one side of each blocking member has an incline. The blocking members are respectively received in the engaging slots and blocked by the projections. A plunger is movably received in the barrel, wherein a front end thereof is movable and abuttable correspondingly against the bottom of the connector, and the front end of the plunger is connected with the bottom of the connector.
