The bacterial flora was investigated in a traditionally fermented mare's milk in Inner Mongolia, China. The initial bacteria count in the collected samples was 1.5-1.7×10⁷/ml for lactic acid bacteria and 3.9-8.0×10⁶/ml for yeasts, and the lactic acid and alcohol concentrations were 1.06-1.28% and 0.5-2.17%, respectively. The bacteria involved in fermentation were found to be lactic acid bacteria and yeasts. A total of 43 isolated strains of lactic acid bacteria were identified which included Lactobacillus rhamnosus (10%), L. paracasei subsp. paracasei (81%), L. paracasei subsp. tolerans (2%) and L. curvatus (7%). Twenty isolated strains of yeasts were lactose-fermenting yeasts, and Kluyveromyces marxianus var. lactis (95%) and Candida kefyr (5%) were isolated.