Klebsiella species are isolated with a relatively high frequency from equines and its environments. Incrimination of Klebsiella micro-organisms as an equine genital infective agent has been documented (Atherton, 1975). Several reports have attributed that Klebsiellas can produce an infection in the uterus of mares and Klebsiellosis in the equine species is a venereal disease as well as the organism can be transferred by mechanical means (Francis, 1975). In Japan, Kamada et al. (1984) isolated K. pneumoniae from 17.8% of 45 samples from cervical swabs of mares suffered from metritis and infertility. Also, Weiss et al. (1976) isolated 712 Klebsiella strains from horses (252 from the nostrils, 289 from prepuce, 78 from the pre-ejaculate, 31 from semen samples and 62 from the cervix mare uteri) and 87.6% of the strains were K. pneumoniae. On the other hand, Brown et al., (1979); Eguchi et al., (1987) and Kikuchi et al. (1988) reported that the incidence of Klebsiellae in prepuce and semen of stallions varied from 2% up to 43%. Furthermore, Greenwood and Ellis (1976) and Weiss et al. (1976) have shown that pathogenic types of the Klebsiella species were in the vestibula, urethra without necessarily infecting the cervix or uterus. The main importance of genital tract infection with Klebsielleae in the equine species is the detrimental effect of infection has on the fertility of breeding stock (Kamada et al., 1984 and Kikuchi et al., 1988). Antibiotics resistance has been encountered with various biotypes of klebsiellas, necessitating comprehensive sensitivity in vitro tests before a treatment is chosen. Marca et al., (1972) observed that most Klebsiella isolates were generally resistant to traditional antibiotics and chemotherapeutics but sensitive to neomycin, nalidixic acid, gentamicin, gabbromycin and kanamycin. Some investigators reported that the pathogenicity of Klebsiellas for mice was not correlated with the presence or absence of the capsule (Marz, 1983 and Eguchi et al., 1987). The objectives in the present study were: (i) to secure the isolation, identification and bio typing of Klebsiellas recovered from genital tract of both mares and stallions, (ii) to test in vitro sensitivity of isolates towards different chemotherapeutic agents and (iii) to compare their pathogenicity in experimentally induced lesions in the mice.