In order to identify the sero-epidemiol. status of major pathogens leading to bovine respiratory disease complex (BRDC) in China, including infectious bovine rhinotracheitis virus (IBRV), bovine viral diarrhea virus (BVDV), bovine parainfluenza virus type 3 (BPIV3) and bovine respiratory syncytial virus (BRSV), 1601 serum samples were collected from 28 dairy farms in 4 provinces and tested by ELISA kit. The results showed that, in general, the pos. rates of antibodies against IBRV, BVDV, BPIV3 and BRSV were 76.2%, 60.5%, 63.2% and 45.4%, resp. at individual level, and 82.2%, 75.0%, 85.7% and 89.3%, resp. at farm level. For different provinces, the rates were 25.1% to 90.3%, 42.3% to 81.3%, 26.9% to 81.1% and 32.2% to 51.9%, resp. at individual level, and 20.0% to 100%, 57.2% to 100%, 75.0% to 100% and 75.0% to 100% at farm level. The pos. detection rates of IBRV, BVDV and BRSV were highest from March to May, and those of BPIV3 remained highest from Dec. to Feb. of the next year. The cows had been infected together by IBRV, BVDV, BPIV3 and BRSV that were prevalent differently in various regions and seasons to certain extent, which indicated that the farms should be further managed to effectively control the four pathogens. In view of the above, some data was provided to prevent and control virus diseases related to respiratory tract in dairy farms.