Strains of Staphylococcus species isolated from bovine mastitic milk at 66 dairy farms in Japan during the period from November 1988 to May 1989 were identified, and examined for their drug susceptibility and β-lactamase production in order to clarify an epidemiological aspect of bovine mastitis caused by staphylococci. The results of bacteriological identification showed that the most predominant species was S. xylosus. Other major species isolated were S. aureus, S. sciuri and S. hyicus. Thirty-eight (71.7%) isolates of S. xylosus, 21 (45.7%) of S. aureus and 5 (71.4%) of S. epidermidis were positive for β-lactamase production. Most of the β-lactamase-producers of S. aureus were classified as high producers, although all of the β-lactamase-positive S. xylosus isolates remained to be low producers. All isolates of S. aureus were sensitive to methicillin and cloxacillin at 6.25μg/ml and 1.56μg/ml, respectively, and none of methicillin-resistant S. aureus were detected. Isolates of other species were considered to be susceptible to 6 β-lactams, in contrast to human isolates, but antibacterial activities of penicillin G and ampicillin were affected more strongly by β-lactamase than those of methicillin, cloxacillin, cefazolin and cefoperazone.