Abstract: This study was conducted to through the light on a recent method for estrus synchronization in lactating dairy cows using PGF2 , GnRH and Estradiol Cypionate (ECP). Four treatments were performed on 60 dairy cows. In treatment 1 (PP), cows received two injections of PGF2 on days 0 and 11 (n = 14); while in treatment 2 (PGP), cows were injected twice PGF2 on days 0 and 11 and 100 ug of GnRH on day 3 after the 1st injection (n=14). In treatment 3 (PGPE-0), cows were treated with PGP and 1 mg of ECP at the same time of 2nd PGF2 injection (n = 16). In treatment 4 (PGPE-1), cows were treated with PGP and 1 mg of ECP one day after 2nd PGF2 injection (n=16). The cows were examined rectally and ultrasonographically by B-mode Ultrasound System [Pie-Medical Scanner-240] with a 6-8 MHz linear rectal transducer. Every cow was blood sampled at selected intervals for progesterone and estradiol assay and inseminated at estrus. The results showed a higher percentage of GnRH-treated cows (PGP) ovulated after 1st PGF2 injection than the non treated (PP) cows (64.3% vs 50%; p< 0.05). The GnRH-treated cows tended to have a larger mature follicle present at 2nd PGF2 injection. Subsequently, the percentage of cows that ovulated after 2nd PGF2 injection was 71.4% vs 50% for GnRH-treated cows than none treated ones, respectively. Two days after 2nd PGF2 injection, cows treated with PGP had a higher peak preovulatory concentrations of estradiol compared to PP treated cows (3.2±0.48 vs 2.6±0.45 pg mL ¹). Additionally, cows treated with ECP (PGPE-0 and PGPE-1) had a higher peak preovulatory concentrations of estradiol (6.3±0.43 and 6.99±0.63 pg mL ¹; p< 0.01); and a higher percentage ovulation (75.0 and 87.5%) than the other treated groups (PP or PGP). Thus, a higher percentage of ECP (specially PGPE-1 group) treated cows were observed in standing estrus and ovulated after 2nd PGF2 injection than the other treated groups. Submission rates (number of inseminated/total�100), differed statistically across treatments, especially those treated with ECP, as well as; the conception and pregnancy rates were observed higher with the ECP treated cows than the other treatments.