[Objective] To understand the infectious status of Histophillus somni（Hs）in cows in Inner Mongolia.[Method] 65 dairy farms in 23 counties of 12 prefecture-level cities were investigated,including 20 large-scale dairy farms,21 small-scale dairy farms and 24 family farms. 2 650 vaginal swabs were collected to detect Hs DNA by fluorescent PCR. [Result] The results showed that 11 cities had positive cases of Hs except for Wuhai City. Moreover,16 of 23 counties have been detected positive cases except for 7 negative counties and the proportion of positive counties was as high as 69.6%. The individual positive rates of large-scale dairy farms,small-scale dairy farms and family farms were 18.2%（182/1 000）,22.9%（240/1 050） and 21.2%（127/600）,respectively,and the positive rates of agricultural areas,pastoral areas and farming-pastoral areas were 15.6%（109/700）,13.5%（135/1 000） and 32.1%（305/950）, respectively. The average individual positive rate was 20.7%（549/2 650）. [Conclusion] This study indicatd that Hs infection was very common in dairy farms in Inner Mongolia,prevention and control should be strengthened.