This experiment was carried out to investigate the effect of reproductive ability on weeks and body weights of broiler breeder males. From 26 to 36 week, volume of semen and body weight were increased. Total concentration was highest at 36 week(P〈0.05), being 21.14$ imes$10(sup)8 cells. Mean of total concentration was 14.66$ imes$10(sup)8 cells and 11.59$ imes$10(sup)8 cells in young(26∼55 weeks) and old(60∼89 weeks) broiler breeder males, respectively. Percentage of fertile eggs, viability and hatchability on weeks were 96.33, 89.55, 86.25% in the young broiler breeder males, 94.84, 91.73 and 86.97% the old broiler breeder males, respectively. The values were not significantly different between the young and old broiler breeder males. While the body weight of cocks was less than 3.5kg, it was not possible to collect semen. Semen collection rate was the best in 4.5∼5.0kg of males, total concentration was highest in 5.0∼5.5kg, volume of semen was highest in 5.5∼6.0kg body weight. More than 80% of the males were in the range of 4∼6kg body weight. Sperm motility was acceptable for breeding.