This study carried out to investigate the genital tract bacterial flora of Thoroughbred mare in Jeju province during March and July, 2006. The specimens were collected from vaginal ucosa and clitorial fossa using a culture swab (BBL, USA) from 100 Thoroughbred mares. Colonies were selected blood and MacConkey agar plate, and identified as standard biochemical properties using Biolog system (Thermo, USA). In this study, 470 gram-negative strains were isolated more frequently than 249 gram-positive strains. We were Isolated Escherichia coli (19.8%), Proteus mirabillis (14.9%), Enterobacter nimipressuralis (7.4%), Enterobacter mobilis (4.7%), Aeromonas encheleia (4.3%), Pseudomonas aeroginosa (3.0%), Staphylococcus aureus (14.9%), Staphylococcus epidermidis (11.2%), Coagulasenegative Staphylococcus spp. (10.0%), Enterococcus faecalis (9.2%), Enterococcus faecium (8.0%), Actinomyces viscosus (7.2%), Micoroccus diversus(6.8%), Streptococcus dysgalactiae subsp. equisimilis(5.2%), Streptococcus equi subsp. zooepidemicus (3.2%), Other non-beta hemolytic Streptococcus spp. (2.0%) and many others from vaginal mucosa and clitorial fossa in Thoroughbred mares. No significant bacteria (Taylorella equigenitalis and Klebsiella pneumonia) were isolated from the mare genital tract. In antimicrobial agents susceptibility test, it shows a high sensibility in the antibiotics of the most which excepts the streptomycin and neomycinm, kanamycin, spectinomycin, compound sulfonamides. Especially, Staphylococcus epidermidis, Enterococcus spp. and Streptococcus spp. were visible a high sensibility in the all antibiotics. However, Staphylococcus aureus, Pseudomonas aeruginosa, Proteus spp. and E. coli were showed a high antibiotic resistance patterns. These results may provide the basic information to establish strategies for the treatment and prevention of reproductive disease in Thoroughbred mares in Korea.