Abstract: Background and Objective: Exogenous GnRH at the onset of estrus or at time of insemination of conventional semen improves fertility. The current study aimed at evaluating reproductive performance of nulliparous Holstein heifers after insemination with sexed semen either with or without GnRH at time of insemination compared to conventional semen. Materials and Methods: A total of 300 heifers were randomly grouped and inseminated at their first natural estrus as follow: (1) Conventional semen (n = 100): inseminated with conventional semen straws (CRV, Netherlands), (2) Sexed semen without GnRH (n = 100): inseminated with sexed semen straws (SiryX®, CRV, Netherlands), (3) Sexed semen with GnRH (n = 100): inseminated with sexed semen straws combined with administration of 10 μg of Buserelin (GnRH agonist, Receptal®) by i. m injection at time of insemination. Results: Conception rate obtained by conventional semen group was significantly higher (p<0.05) than sexed semen without GnRH group (63 vs. 49%), while it was comparable to the value obtained by sexed semen with GnRH group (54%). Number of services per conception, gestational length and incidence of dystocia showed no significant difference among heifers (p>0.05). Conclusion: Therefore, conception rate of conventional semen is superior to sexed semen, however, administration of GnRH at time of insemination of sexed semen can improve its fertility output to a similar level.