A syringe assembly includes a syringe, a locking element and a protective sleeve. The syringe includes a needle connected to a cylinder. The protective sleeve is located on and around the cylinder and movable from a first position into a second position. The protective sleeve only covers the cylinder in the first position. The protective sleeve covers the needle in the second position. The locking element is adapted to keep the protective sleeve in the first position in a resilient manner. The locking element is further adapted to keep the protective sleeve in the second position. That is, after the protective sleeve is moved to the second position, return of the protective sleeve to the first position is prevented by the locking element.
