Abstract: In order to find the pathogen of acute death of dairy cows after giving birth in a dairy farm in Henan Province（nucleic acid tests of early bovine epidemic fever virus, bovine viral diarrhea virus and bovine infectious rhinotracheitis virus were negative, and Clostridium in intestinal contents and Pasteurella in lung were negative）, in this experiment, the spleen, liver and other tissues and blood samples of sudden death cows were collected for bacterial isolation and culture, Gram staining microscopy, biochemical identification, PCR amplification and sequencing of 16S rRNA gene, and drug susceptibility test and pathogenicity test. The results showed that one strain of bacteria was isolated from cow blood samples, and the Gram staining microscopic examination of this strain was blue-purple and arranged in a grape-like pattern, which was consistent with the biochemical characteristics of Staphylococcus sciuri; its 16S rRNA gene sequence was highly homologous to Staphylococcus sciuri in GenBank database, with a similarity of more than 99.7%, which confirmed that the isolated strain was Staphylococcus sciuri, named HNSX-B1. The HNSX-B1 strain was sensitive to cephalosporins（cefazolin, cefradine and ceftriaxone）, quinolones（norfloxacin, ciprofloxacin, and ofloxacin）, tetracyclines（tetracycline, doxycycline, and minocycline）, and gentamicin, erythromycin, piperacillin, oxacillin, moderately sensitive to ampicillin, ceftazidime, neomycin, and aminoglycosides（kanamycin, clindamycin）,and resistant to penicillin and cotrimoxazole. Mice all died after 36 h of infection with HNSX-B1 strain（1×10~9 cfu/mL, 200 μL）. The results suggested that one strain of Mammaliicoccus sciuri with obvious pathogenicity to mice was successfully isolated, which might be the pathogen causing acute death of postpartum cows in the dairy farm.