Wounds infection is pathogen-infected to the point where it triggers a local and systemic reaction in the host. Multiple pathogens typically colonize wounds, and Pseudomonas aeruginosa has a higher prevalence in wound infection. This study tried to assess the immune response by measuring the level of complement fragment C5a in the serum of rats that induced wound infected with Pseudomonas aeruginosa. The animal was divided into three groups ( infected wound , wound without infection, and healthy control ) and the procedure was performed by inducing 10 mm excisional wound on the dorsal region of rats and after 24h from inducing wound contaminated the wound region in the infected group only with bacterial suspension that contains 2.5 ×106 CFU of P. aeruginosa. Then at specific determined time points (24hrs, 48hrs, 72hrs) after infection blood samples and skin biopsy samples were collected. By using ELISA kitt sandwich methods we found that C5a is highly elevated in the infected group in comparison with other animal groups. And the histological section showed no signs of inflammation during 24hrs while necrosis of the dermis layer was observed after 48hrs and 72hrs.