A syringe with a blocking structure includes a one-way engagement unit 5, 6, 7 having a propping portion 51, 61, 71, a flange 23, 24, 25 extended outwardly from a rod 4 and abutted with a cylindrical body 2, and a flexible bracket 52, 62, 72 extended outwardly from the rod 4 and isolated from the propping portion 51, 61, 71, and the flexible bracket 52, 62, 72 has an external diameter greater than the propping portion 51, 61, 71. When the rod 4 is moved forward with respect to the cylindrical body 2 to pass through the flange 23, 24, 25, the flange 23, 24, 25 abuts the flexible bracket 52, 62, 72 to tilt backward. When the rod 4 is moved backward with respect to the cylindrical body 2, the flange 23, 24, 25 abuts the flexible bracket 52, 62, 72 to tilt the flexible bracket 52, 62, 72 forward, and the propping portion 51, 61, 71 blocks the flexible bracket 52, 62, 72.一種具有卡退結構的推桿，適用於搭配一筒體，該筒體包含一凸緣，該具有卡退結構的推桿包含一桿體，及一單向卡退單元，該單向卡退單元包括一頂抵部，及一撓折活瓣片，該頂抵部自該桿體向外延伸並能夠觸抵該凸緣，該撓折活瓣片自該桿體向外延伸且與該頂抵部相間隔，藉此，該撓折活瓣片外徑大於該頂抵部外徑，該桿體相對該筒體朝前推移穿過該凸緣時，該凸緣頂抵該撓折活瓣片朝後傾斜，該桿體相對該筒體朝後推移時，該凸緣頂抵該撓折活瓣片，使該撓折活瓣片朝前傾斜，該頂抵部擋住該撓折活瓣片。
