Abstract: Mastitis is one of the most frequently observed diseases in dairy cow farms in China.This disease seriously affects the milk yield and dairy products quality and causes high economic losses in the dairy cow population.There is evidence that nutrients deficiency can increase the risk of subclinical mastitis in dairy cow.Trace element selenium is reported to be able to improve immune function of the mammary gland,which is of great significance to the udder health and subclinical mastitis control in dairy cows.This article elaborates the association of selenium deficiency with occurrence of subclinical mastitis in dairy cows,in hoping to provide useful information for preventing this disease through regulating the udder immune function.