The aim of this study was to compare the effectiveness of GnRH and PGF2α combination, and PGF2α and PGF2α regimens for synchronization of estrus in cows. The study was carried out on 20 (6 Brangus, 14 Brown Swiss) cows, age ranging 3 - 5 years old. The cows were randomly devided into two groups. In group I (n=10), cows were treated with an intramuscular injection of 20 µg GnRH (day=0) a random stage of the estrous cycle, followed by PGF2α 7µg days later (day=7). in group II (n=10), cows were given two injections of PGF2α 11 day apart (day= 0, and 11). The cows were observed to determine the onset of the estrus for four days and then inseminated 12 hours after the onset of estrous. Blood samples were collected to determine plasma progesterone levels, in group I on the day ol GnRH and PGF2α injections and at estrus. and in group II on the day of each injection of PGF2α and at estrus. The mean interval from synchronization to onset of estrus, synchronization and pregnancy rates of the groups were determined. Plasma progesterone ievets on days 0 and estrous were similar (p > 0,05) between the two groups, but on the day of synchronization, in group İ were found to be higher progesterone levels than in group 11 (p < 0.01). The mean interval from synchronization to estrus in group I and II were found 54,3 ± 3.2 and 62.2 ± 3.2 hours, respectively (p> 0.05). The synchronization rate were higher in group I (% 100) than in group II (% 80) (p< 0.01), and pregnancy rate of the group I and II were % 60 and % 40 respectively (p< 0.05), The distribution of the estrous in group I concentrated between 40 and 60 hours following the synchronization, but in group II were a homogen distribution between 40 and 80 hours after the synchronization. As a conclusion, application of a GnRH analogue prior to synchronization of estrus with an injection of PGF2α may provide higher results than two injections of PGF2α lor estrus synchronization in cows.