Abstract: To investigate effects and source of pathogens causing bovine mastitis on microbial community in milk, 16S rRNA sequencing technology was employed．Samples were collected from cows with mastitis and healthy cows at a dairy farm in Yantai City, Shandong Province, as well as from milking parlour, cowshed air, and feces．Microbial community structures were compared, and sources were traced using SourceTracker．Results showed that milk of cows with mastitis increased bacterial abundance but reduced diversity. Samples from the same source had similar compositions, while significant differences were observed among samples from healthy cows, mastitis-affected cows and faeces．Moreover, results indicated that Streptococcus uberis was the main pathogen causing mastitis at studied farm, with changes in milk microbiota following mastitis．Source tracking with SourceTracker suggested that pathogens mainly originated from milking parlor environment．These results provide a theoretical reference for prevention and control of mastitis in dairy cows．