Abstract: OBJECTIVE To explore the protective activity of recombinant mouse beta defensing 3(rMBD3) in influenza A virus infected mice. METHODS Mice were intraperitoneal injected with 10 mg·kg^-1·d^-1 rMBD3. Three months later the general condition of mice were observed. BALB/c mice, ♀, were divided into five groups: normal control group, model control group, rMBD3 high dose group(10 mg·kg^-1·d^-1), rMBD3 low dose group(5 mg·kg^-1·d^-1) and ribavirin (100 mg·kg^-1·d^-1) group. The H1N1 infected model was established by influenza virus nasal drip. The mice were given drugs by intraperitoneal injection after infected for 12 h. The weight and survival of mice were surveyed daily. On the 3rd day, the virus titer in bronchoalveolar lavage fluids, lung index and the histological patterns of major organs were observed. The serum interferon-γ was determined by ELISA kit. RESULTS There was no abnormal reaction or death of the mice after injected 10 mg·kg^-1·d^-1 rMBD3 for 3 months. Obvious pathological changes of each important organs were not found. Each dose group of rMBD3 reduced the influenza virus titer in bronchoalveolar lavage fluids, lung index inhibition and lung tissue pathological changes. CONCLUSION rMBD3 shows no obvious toxic effects in mice, and has the activity of anti-influenza virus in vivo and protection of the mice with influenza.