The aim of this study was to determine the effects of two dietary protein levels on testosterone, testicular parameters and semen quality in Kivircik ram lambs during pubertal development. Two experimental groups were formed. Following weaning, crude protein (CP) and metabolic energy (ME) levels were 12% CP, 2.54 Mcal/kg in group I (low protein diet) and 18% CP, 2.52 Mcal/kg in group II (high protein diet). Measurements of live weight and testicular characteristics and collection of blood samples for testosterone hormone concentrations were performed at 20 day intervals starting from 115-days- up to 195-days-of-age. There was an increase in semen volume, spermatozoa concentration and the percentage of progressively motile sperm in both groups between 135 and 195 days of age. Group I had significantly higher semen volume on day 175 (P < 0.05). Furthermore, spermatozoa concentrations were higher in group I than those in group II on days 155 and 175 (P < 0.05). Values of live weight, testicular diameter, testicular circumference, testicular length and testicular volume of ram lambs in group II (high protein diet) were higher than those in group I (low protein diet). Testicular length and testicular volume of group II were significantly higher than those of group I on day 195 (P < 0.05). Despite the fact that group II had an alternating testosterone hormone concentration, it was determined that Group II had better testosterone hormone concentration values than group I on day 115, 135 and 175. However, group I had a higher testosterone hormone level on day 155 and 195. Live weight and testicular characteristics of ram lambs fed with a high protein diet were affected positively during pubertal development. However, it was observed that feeding with a high protein diet had a negative effect on semen characteristics by impairing the thermoregulation mechanism and spermatogenesis in testicles because of excessive fat accumulation in the scrotum.