These experiments were investigate the effects of bacterial infection of uterus and vagina during bovine embryo transferring on the development of embryo. We examined the distribution of reproductive disordered cow by akind of disease, identified the bacteria isolated from the vagina of those cows and bacterial infectin of media and its treatment with several kinds of antibiotics at that. The results obtained were summarized as follows ; 1. The total 592 reproductive disordered cows were caused by ovarian dysfunction(43.4%), ovary-uterus complication(24.5%), endometrities(17.7%), and repeat breeder(12.0%). 2. The main bacteria among 11 kinds of bacteria(113 colonies) was E. coli(38 colonies, 33.6%). Likewise, E. coli was propotioned to 23 and 22.7% among bacteria from vagina of endometritis and repeat breeder, respectively. 3. The sensitivities of viginal bacteria to pencillin and streptomycin were 6.2 and 4.4% respectively, but those to gentamycin and chloramphenicol were 22.1 and 16.8%, respectively. The similar sensitivities were found in the embryo recovery media. 4. The rates of bacterial infection of recovery medim and that of abnormal development of embryo were 75 and 80%, respectively. 5. The antibiotic sensitivity assay of ova recovery media showed gentamicin and chloramphenicol gave better results than streptomycin and penicillin. 6. The developmental rate of 1-cell stage mice embryos was 34.0% in bacterial infected culture media, but was 40.0, 58.0, 40.0 or 30.0% with the treatment of kanamycin, gentamycin, chloramphenicol, streptomycin, or penicillin, respectively.