Abstract: A syringe includes a barrel with a plunger movably inserted therein and a needle set is connected to a neck extending from an end of the barrel and includes a needle. A cone-shaped member extends radially outward from the needle. A cap has an insertion end for receiving the needle and a close end. A positioning device is connected to the cap and includes a plurality of first plates and second plates extending inward from the inner periphery of the cap. After use, the needle penetrates through holes enclosed by the first and second plates and the cone-shaped member is positioning between the first and second plates. Due to the holding of the cone-shaped member between the first and the second plates, the cap can not be removed from the needle and enhance the safety to recycle the syringes.