It is reported that an rate infection with Pasteurella Pneumotropica in clean KM mice.The study included clinic and pathologic observation,pathogenic diagnosis and prevalence survey.It was observed that morbidity was 3.8% in the infected mice.The sick mice with the age about 3 weeks showed the normal general condition,but conjunction,little pus swelling in eye rim when autopsy was observed.Pasteurella pneumotropica was isolated from the pus swelling only and the biologic characteristic with hemolysis and Indol test (-) in some strains,was also found.The infection rate is different in each age group of the mice,which 80% in old age group,90% in 5-6 weeks and 100% in 3-4 weeks age group of the mouse.It is indicated that the young have higher sensitivity than the mature in the mice.