The present study was designed to investigate the effects of PGF2¿ or GnRH injections during postpartum on uterine involution, length of postpartum period, number of services per conception, days open and calving interval in cross-bred Sudanese dairy cows. The findings of this experiment explained that the injection of GnRH significantly shortens the time needed for uterine involution, postpartum period, days open and calving interval as compared with control (P < 0.005, p < 0.05, P < 0.001 and P < 0.001 respectively). Moreover, the number of services per conception was improved significantly (P < 0.04). It is concluded that the use of PGF2¿ or GnRH during the first, second or third week postpartum improves the reproductive efficiency of cross-bred dairy cows. Thus a calf per cow per year can be produced if this regime is employed. However, a single injection of PGF2¿ as early as 7 days has no effects on the above parameters.