Growth hormone (GH) is secreted by the anterior pituitary gland and presence of growth hormone receptors has been reported in the mammalian reproductive tract. Growth hormone through these receptors has direct and indirect action on the mammalian reproductive system and affects the semen parameters. This study was aimed to evaluate the effect of the exogenous recombinant bovine somatotropin (rbST) on libido, pre and post freezing semen parameters of Cholistani bulls. For this experiment six Cholistani bulls were selected from Semen Production Unit, karaniwala Bahawalpur. The animals were randomly divided into two groups, a treatment (n = 3) group and b control (n = 3) group. The experimental group was given 500 mg s/c of rbST (Boostin) weekly from 1 nd week up to 13 th week. Libido of each bull was assessed in terms of reaction time. The semen samples were collected throughout the experiment twice a week and were evaluated for volume, sperm motility, viability, functional membrane integrity and concentration. The mean values of Cholistani bulls for libido (sec), semen volume (ml), mass activity (1-5) and sperm concentration (million/ml), were (50.1±10.8 vs 45.12 ± 9.5), (4.83±0.13 vs 3.83±0.1), (2.83 ± 0.03 vs 2.29 ± 0.02) and (1138.1±27.7 vs 920.8±21.2) in treated and control groups respectively. Pre-freezing % sperm motility, post-freezing % sperm motility, pre-freezing % live spermatozoa, post-freezing % live spermatozoa, pre-freezing functional membrane integrity and post-freezing functional membrane integrity were (70.97 ± 1.07 vs 67.15 ± 1.46), (49.82 ±1.08 vs 45.62±1.36) (77.35 ± 0.42 vs 72.07 ± 0.37), (62.94 ± 0.41 vs 54.06 ± 0.45) (76.06 ± 0.33 vs 69.85 ± 0.43) and (59.05 ± 0.48 vs 55.27 ± 0.44) in treated and control groups respectively. All semen parameters of Cholistani bulls affected by rbST treatment significantly.