The invention discloses a fixing device for fixing testicles of rats for injection, which includes a positioning tube, one end of the positioning tube is tapered, and a bearing platform is set at the other end, a binding piece is set in the positioning tube, and A sliding groove is provided on the carrying platform, and a collision seat is arranged in the sliding groove, and a collision cam is rotated on the collision seat, and a hole seat is provided on the carrying platform, and a hole seat is oscillatingly arranged on the hole seat. U-shaped elastic restraint arm, the two free ends of the elastic restraint arm are bent to form pins, the pins are inserted into the hole seat, and the elastic restraint arm is closely attached to the mating surface of the outer wall of the hole seat A first positioning groove, a first converging protrusion, a second positioning groove, a second converging protrusion and a third positioning groove are formed, and the second positioning groove is deeper than the first positioning groove and the third positioning groove. The overall structure is simple, and the testis of rats can be fixed, thereby facilitating cell transplantation experiments.