The present invention discloses a safety syringe and a safety mechanism for use in the safety syringe. In one example, the safety syringe comprises: a barrel having a proximal end, a distal end and a cavity being between the proximal end and the distal end and defining a longitudinal axis, a needle holder extending distally from the distal end; a plunger having a distal portion inserted inside the barrel from the proximal end of barrel and a proximal portion located outside the barrel; a needle having a proximal portion inserted into a needle passage of the needle holder from the distal side of the needle holder and a distal portion located outside the needle holder, the needle being hollow and in fluid communication with the cavity of the barrel; and a safety mechanism mounted at least partially around the needle holder; at an unactuated position of the safety mechanism, the distal portion of the needle is not covered by the safety mechanism; at an actuated position of the safety mechanism, at least distal tip end of the needle is covered by the safety mechanism to prevent accidental contact with the distal tip end of the needle. According to the present disclosure, it is feasible to, upon assembling the syringe, first duly mount the safety mechanism, and then mount the needle. As such, the needle needs to be calibrated only once, and furthermore, the safety mechanism, before being actuated, does not interfere with the needle.