A probiotic lactic acid bacterium, named LC577, was isolated from Tibetan kefir. This bacterial strain was identified as Lactococcuslactis casei based on its morphologic properties, 16S rRNA sequence analysis and physiological and biochemical characteristics. The strain had a strong ability to produce acid, and produced a cheese-like aroma after fermentation in skim milk. In addition, it showed tolerance to acid and bile. After 4 h culture in a simulated gastric fluid, the viable count increased slightly, but decreased to 6.15 × 105 CFU/mL after exposed to 3 g/L oxgall for 4 h.