Objective To test our hypothesis that sensitivity to avian influenza A(H5N1)virus varies among mouse strain backgrounds, we compared the pathogenicity of H5N1 viral infection in 5 mouse strains. Methods Onehundred-fifty mice from 2 inbred strains(BALB/c and C57BL/6), and 3 outbred stocks(ICR, NIH Swiss, and KM Swiss)were used. Thirty mice of each strain were subjected to an infected group(20 mice), in which mice were inoculated with 0. 1 mL(104.875 TCID50)of A/Goose/Guangdong/NH/2003(H5N1)virus intra-nasally; ten control mice received noninfectious allantoic fluid. Clinical signs were assessed daily for 14 days post-infection. Necropsy was performed on mice that died during the experiment and those euthanized at end of study. Tissue samples were collected for viral isolation and pathological analysis. Results H5N1 virus infection can cause respiratory illness in all 5 strains with severe or minor acute respiratory distress symptoms, but with different mortality rates: 70% in BALB/c; 50% in ICR; 40% in NIH Swiss; 25% in C57BL/6; and 10% in KM Swiss mice. Necrotizing interstitial pneumonia was found in all cases of death. The virus was isolated from the lungs of all infected dead mice. Conclusion A/Goose/Guangdong/NH/2003 (H5N1)virus can infect all mouse strains used in this study, and can cause clinical symptoms and pathological changes similar to those found in humans infected with HSN1 viruses. However, the pathogenicity of H5N1 viral infection varies significantly between the different mouse strains. Thus, in future study of H5N1 virus infections the mouse strain most relevant to their particular research purpose should be selected as animal model.