The objectives of this study were conducted to compare pregnancy rates of pubertal heilers inseminated at natural estrus and senchronized estrus with PGF2o, and to determine whether the positive effect of GnRH administrations after insemination on fertility of pubertal heifers. A total of 114 pubertal heifers at the age of 11-13 months were used. Heifers were randomly allocated to four groups. Pubertal heilers in Group NE (n=29) and Group NE+G (n=28) were inseminated artificially approximately 12 h after the onset of natural estrus. Pubertal heifers in Group SN (n=29) and Group SN+G (n=28) were synchronized using two injections of 0.5 mg eloprostenole (Estrumate^®) given 11 d apart and were observed from 36 to 108 h alter second injection of PGF_2a. They were inseminated artificially approximately 12 h after detection of estrus. In addition, heifers in Group NE+G and group SN+G were given 0,1 mg gonadorelin (Ovarolin^®) immediately after insemination. Heifers were observed for estrus between 19 and 21 d after insemination. Estrus rate of sencronized pubertal heifers was determined as 78,9%. First service conception rate was observed to be significantly lower {P=0.011) in heifers in group SN than the heifers in group NE {45.8% vs 79.3%). Although sencronized pubertal heifer treated with GnRH (group SN+G) showed a increase in pregnancy rate compared with group SN, there was no significant difference (P=0,083) in conception rate between group SN+G and Group SN (71.4% vs 45.8%). These results indicate that there was a significant decrease m conception rate at first service for pubertal heifers synchronized with PGF_2a. However, GnRH given after insemination to senchronized pubertal heifers might affect positively on fertility, (hough it did noi significantly increase conception rate.