The relationship between the prepubertal body weight, testicular size, testosterone concentration, and postpubertal reproductive function was investigated in Kivircik ram lambs. The body weight, testicular size, and testosterone concentration were measured every 20 days between 60 and 420 days of age. Semen was collected from the ram lambs at 7, 8, 9, 10, 11, 12, 13 and 14 months of age. Data obtained were analyzed by best subsets regression model. We determined that body weight, scrotal circumference, testicular length, and testosterone levels in the early prepubertal period (days 80, 100, and 120), when combined with each other, allow the determination of the postpubertal (days 220, 240, 260 and 280) testicular diameter.