A syringe is provided, including: a barrel, a needle assembly and a plunger. The barrel has a front end portion thereinside. The needle assembly has an opening region which has a first blockable portion extending laterally. The plunger is slidably assembled to the barrel and has a second blockable portion at an end facing toward the front end portion. When the plunger moves toward the front end portion, the first and second blockable portions are blocked with each other.本發明關於一種注射器，其包括一注射筒、一針具組及一推桿。該注射筒內設有一前端部。該針具組之一端具有一開口區，該開口區橫設有一第一卡部。該推桿滑設於該注射筒，該推桿朝向該前端部之一端設有一第二卡部。其中，當該推桿朝該前端部滑移時，該第二卡部即與該第一卡部相卡扣。
