Objective To define dynamic changes of viral loads and antibody responses in ICR mice naturally infected with hepatitis virus in an MHV contaminative facility. Method A total 50 ICR were housed by different "dirty bedding" exposure.Antigen and antibody was detected after 2，4，8，14，21，28，35，42，56 and 84 days. Result Mouse hepatitis virus (MHV) was detected in lung after 2 days, and positive rate is 20% (1/5). MHV was detected in lung, liver, cecal and feces during 4 and 56 days. The positive rate was 0/5 in lung, liver, cecal and feces on 84 days after experiments. Antibody positive rates were 100% during 8 and 84 days. Conclusion Serological method can be used as the main method for the diagnosis of the daily supervision, and antigen detection method can only be applied to early diagnosis.