At 43 days of age, 246 broiler breeder males were randomly assigned to either a 9, 12, or 15% protein diet (isocaloric) fed on a restricted basis until birds were 50 wk of age. Birds fed the 15% protein diet served as the control group for maintaining body weight. All groups received equal quantities of feed. Semen production was monitored weekly from 17 through 49 wk of age. Semen was evaluated for volume, concentration, and number of spermatozoa per ejaculate during four periods: 25 through 30, 36 through 37, 42 through 43, and 48 through 49 wk of age. Carcass composition and testes weight were sampled at 22 and 28 wk; at 50 wk of age all remaining males were analyzed. The dietary protein effect on body weight was linear (P less than .05). Birds fed the 9% protein diet had the lowest weights, while birds fed 12 and 15% protein became similar in body weight with increasing age. Semen volume, concentration, number of spermatozoa per ejaculate, and testes weight were unaffected by dietary protein level. The percentage of males that produced semen when fed the 9% protein diet was greater (P less than or equal to .09) with males fed 12 and 15% dietary protein. Dietary protein had a significant negative linear effect (P less than or equal to .001) on percent carcass fat at 50 wk of age but no effect on percentage carcass protein. Reducing dietary protein to 9% decreased male body weight slightly, increased carcass fat, and had no adverse effects on semen production through 50 wk of age.