Objective In order to determine the pathogenic bacteria causing bovine mastitis in a dairy farm in Xichang，Method Two milk samples were collected from dairy cows with mastitis for isolation. The isolated strain was further identified by morphological observation， biochemical identification， khe and 16S rRNA gene identification， mice pathogenicity test and drug resistance analysis.Result （1） One strain was isolated， which was gram-negative bacterium， with shot rod-shaped under microscopic examination. The results of morphological identification and biochemical characteristics were consistent with Klebsiella pneumonia. （2） The sequence homologies of khe and 16S rRNA genes and K. pneumonia in GenBank were 99.6 %~99.8 % and 99.7 %~100 %， respectively. Therefore， the isolated bacteria can be identified as K. pneumonia and named XC1. （3） The results of the mice pathogenicity test showed that all four mice died on the third day of inoculation， indicating that the isolate of XC1 had strong virulence. （4） The drug sensitivity test results showed that the isolate of XC1 was highly sensitive to enrofloxacin， norfloxacin， cefepime and ceftazidime； moderate sensitive to tobramycin， gentamicin and neomycin； and resistant to erythromycin， ampicillin and amoxicillin.Conclusion The results of this study demonstrated that the occurrence of mastitis on the dairy farm was associated with Klebsiella pneumonia infection， and the isolate of XC1 showed different degrees of resistance to commonly used antibiotics.