Abstract: 2 391 bovine serum samples were collected from 17 dairy farms of Inner Mongolia to detect the antibody level of bovine viral diarrhea-mucosal disease by ELISA. The antigen detection of bovine viral diarrhea-mucosal disease was made on 222 antibody-negative serum samples by ELISA. The results showed that positive BVDV antibody was detected in 17 dairy farms. And there were 2 125 positive serum samples,and the highest positive rate was 100%and the lowest positive rate was 46.8%and the average positive rate was 88.9%. BVDV antigens in 14 dairy farms were detected and that in 5 dairy farms were positive. The positive rate was 3.6%（8/222）. It was shown that the bovine viral diarrhea generally existed in dairy farms of Inner Mongolia with higher infection rate. And persistent infection （PI） cattle were existed in cow herd.