To synchronize estrus and ovulation for improving pregnancy rate (PR) of repeat-breeder buffaloes, Controlled Internal Drug Release (CIDR) + prostaglandin (PGF2α) was used before service of repeat breeder buffaloes. Total of 20 cyclic lactating buffalo-cows (4-7 years, 400-500 kg, non-pregnant up to 90-postpartum day) and 10 cyclic buffalo-heifers (2.5-4 years, 350-400 kg, not conceived after 3 services) were used in this study. In the 1^st group, a CIDR was inserted for 9 days, regardless reproductive status, and then animals were intramuscularly injected with PGF2α 24 h prior to CIDR removal. In the 2^nd group, control animals were used at the same interval. Animals in heat were naturally served and blood samples were collected on different days post-service for serum P4 determination. Pregnancy was diagnosed on day 25 post-service. Results showed that overall mean of PR was higher (P<0.01), while serum P4 at estrus was lower (P<0.001) in CIDR than in control, but both parameters were not affected significantly by animal type or CIDR x animal type interaction. Serum P4 at estrus was lower (P<0.05) in pregnant than in non-pregnant, regardless treatment or animal type. At the following post-service days, serum P4 showed the same trend of change, being higher (P<0.001) in CIDR than in control animals and in pregnant than in non-pregnant animals, regardless animal type. It could be concluded that the random usage of CIDR device for 9 days and prostaglandin F2α injection 24 h pre-CIDR withdrawal can be applied to improve pregnancy rate of repeat breeder Egyptian buffaloes.