Objective was to determine the effects of adding a gonadotropin-releasing-hormone (GnRH) treatment at the beginning and/or at the end of an estradiol-based protocol for timed artificial insemination (TAI) on pregnancy per AI (P/AI) in Nelore (Bos indicus) cows. The experiment was conducted in 2 beef cattle farms (A and B) located in a central-western state in Brazil. The body condition score (BCS) evaluation and the ultrasound examination to determine ovarian status (follicle diameter <10 mm; ≥10 mm; or presence of corpus luteum - CL) were performed at the beginning of TAI protocol. Cows (n = 494) were randomly assigned to 4 groups: Control (n = 126), GnRH at day zero (D0) of the protocol (n = 123), GnRH at d 10 (D10) (n = 123), and GnRH in both times (D0+D10) (n = 122). The GnRH treatment consisted of one 50 µg i.m. injection of gonadorelin. All the cows were submitted to the following TAI protocol: Day 0 = insertion of intravaginal progesterone device previously used for 8 or 16 d and 2.0 mg of estradiol benzoate (EB) i.m.; Day 8 = progesterone device withdrawal, 750 IU i.m.injection of equine chorionic gonadotropin (eCG), 1.0 mg of estradiol cypionate (ECP) i.m. and 0.265 mg of sodium cloprostenol (PGF_2α) i.m.; Day 10 = TAI, performed by a single inseminator. Pregnancy was diagnosed by ultrasound 39 ± 10 d after TAI. Data were analyzed by GLIMMIX procedure of SAS. Overall P/AI was 42.7%. No effect of treatment was detected (P = 0.25) on P/AI, and it was 37.3% for Control, 45.5% to GnRH D0, 49.6% to GnRH D10 and 38.5% to GnRH D0+D10. An effect of farm was detected on P/AI, where Farm A had 47.3% and Farm B 38.2% (P = 0.02). Cows with follicles <10 mm had lower P/AI (16.4%; P < 0.01) than cows with follicles ≥10 mm (46.2%) and the ones that had a CL (48.4%). The interactions between farm and treatments (P = 0.77) or between ovarian status and treatments (P = 0.12) did not affect P/AI. In conclusion, gonadotropin-releasing-hormone treatment used at the beginning and/or at the end of an estradiol-based TAI protocol did not affect pregnancy per AI in Nelore (Bos indicus) cows.