The effectiveness of prosaposin as a neurotrophic factor was investigated using rats with bilateral stab wounds, injecting 240 ng per day of prosaposin for 3 days. In Morris water maze task, after 3 weeks postoperation, the stab-wounds rats show significant impairment in acquisition compared with the sham-operated rats. In the transfer test the mean number of crossings of the platform place in stab-wounds was significantly lower than that in sham-operated rats (P < 0.01). The stab-wounds rats treated with prosaposin showed significant improvement (P < 0.05). The cavities following stab wounds in the rats treated with prosaposin were significantly smaller than those in the rats treated with (P < 0.05). Our data support that prosaposin is likely to be a new agent for brain injury.