Background: Seasonal anestrus, which is controlled by the photoperiod in ewes, limits the ability to the fertility of ewe every time. Therefore, using hormones by vaginal devices is the most effective way of increasing fertility in order to form oestrus during the anestrus period and obtain a high rate of pregnancy. But, vaginal devices may cause a change in the profile and number of bacteria in the uterus and vagina, and thus create an environment suitable for infection. For this reason, identification of bacteria that are the source of infection can be achieved by performing antibiotic susceptibility tests and interpreting them correctly. The purpose of this study was to characterize the effect of intravaginal device-type and treatment-duration on vaginal bacteria count and type and determine the antibiotic susceptibility of vaginal bacterias in ewes after a program of oestrus synchronization. Methods: A total of 90 clinically healthy Kivircik ewes were selected. In order to provide oestrus synchronization during anestrus season (June), CIDR was inserted intravaginally to 45 ewes, the other 45 ewes were progestogen sponges inserted. In both groups remained inserted for 5, 9 and 13 days. While vaginal devices were withdrawal both groups ewes were exposed to intramuscular 350 IU PMSG injection. The mucous samples were collected from all ewes 0, 5, 9 and 13 days at time the IVS or CIDR withdrawal. In samples, bacterial concentration, bacterial identification, and antibiotic susceptibility were determined. Result: The changes in the vaginal flora caused by the vaginal devices favored the development of opportunistic microbiota that could potentially be pathogenic. In the study, after vaginal device withdrawal, the bacteria species most frequently observed in both IVS and CIDR groups were E. coli. According to the results of this study, the first choice of antibiotics for vaginal infections caused by G- agents in ewes should be any of AXC, CEP and CTZ compared to other antibiotics.