This study was carried out at Mehallet Mousa Experimental Stations, belonging to Animal Production Research Institute to evaluate the effects of methergin or oxytocin administration at 0 or 24 hours after calving on uterine involution and the pregnancy rate of buffalo cows. About 20 multiparous Egyptian buffalo cows with normal parturition having (400-650 kg) live body weight, (2-7) parities and (2.5-3.5) body condition score were used in this study. Animals were divided into five groups (n=4/each). Animals in the 1^st group were i.m. injected with saline solution at calving and 24 h post-calving (control). Each animal in the 2^nd and 3^rd groups (G2 and G3) received an i.m. injection of 3 mg methergin (MET) at 0 and 24 h post-calving, respectively. While, each animal in the 4^th and 5^th groups received an i.m. injection of 100 IU oxytocin (OXY) at 0 and 24 h post-calving, respectively. Throughout post-partum period, all buffaloes were hand milked twice daily. Routine examination of the genitalia per rectum was conducted twice weekly to judge the uterine involution manually by fingers. Ultrasonography was used immediately after rectal palpation to determine gravid and non-gravid uterine horns and cervical diameter. Uterine involution was considered complete when both horns were nearly symmetrical. Pregnancy was diagnosed by rectal palpation on day 45 post-insemination and conception rate was recorded. Results revealed that the duration of symmetric horns was shorter (P<0.05) for MET at 0 or 24 h post-calving than that in the controls. The same duration tended to reduce in OXY at 0 or 24 h post-calving as compared to the controls, but the differences were not significant. The duration of cervical closure was insignificantly lower in treatment groups, being the shortest in MET at 0 h. The significant reduction in gravid horn diameter stopped on day 17, 17, 24 and 24 of post-partum period in MET 24 h, MET 0 h, OXY 0 h and OXY 24 h versus on day 27 of post-partum in the control ones. The significant reduction in non-gravid horn diameter stopped earlier in MET 0 h (day 7) than in other treated and control groups (day 14). The significant reduction in cervical diameter stopped earlier in MET 0 h (day 14) than in other treatments and control (day 17). Animals treated with OXY at 0 h showed the best results regard to conception rate, number of services per conception and days open. In conclusion, it was found that the oxytocin treatment at 0 h of calving performed on buffalo cows with the purpose of stimulating involution had pronounced effect on the duration of days open, number of services per conception and conception rate, without marked effects on the shrinkage of the uterine horns diameter and closure of the cervix during post-partum period compared with that seen in the control.