In this study, the forelimbs' muscle, one of the important parts of chicken body for meat production, was compared quantitatively with its weight among various breeds and sexes. Males and females of Rhode Island Red (RIR), Barred Plymouth Rock (BPR), White Leghorn (WL) and males of White Cornish (WC) were used. The experimental period was from 2 to 18-19 weeks of age. Weighing of skeletal muscle was done in the forelimbs' part and its four different subparts (shoulder girdle, brachium, antebrachium and abdomen). Regression equations of males and females of each breed were calculated between the muscle weight of these parts and live weight or total muscle weight. And these equations were applied to the study of ability of meat production. The results were as follows: Specific individual ability of meat production in the forelimbs' part and its four subparts was observed among all breeds and sexes. This individual ability was controlled by two factors: one was the rate of increase of the live weight, and the other was the rate of increase of the individual muscle percentage weight against the live weight. In males, it was supposed the ability of meat production of the forelimbs' part was best in WC among all breeds. Although the percentage weight of forelimbs' muscle of WL exhibited about the same high value as that of WC until 2kg of live weight, it was not always said that WL was a good meat producer in the forelimbs' part, for its rate of increase of live weight was smallest of all breeds. RIR and BPR showed the smallest rates of increase of the muscle percentage weight. But these breeds seemed to be better meat producers in the forelimbs' part than WL because of those larger rates of increase of live weight. In females, the results were as same as those of males among all breeds. Between sexes, the percentage weight of forelimbs' muscle of females increased more rapidly than that of males in all breeds. The percentage weight of forelimbs' muscle to total muscle weight did not change in WL females, and decreased in WL males and all other breeds. This suggests that the ability of meat production of forelimbs' part falls behind that of other parts in the body. When forelimb was divided into four subparts, the ability of meat production of each subpart was also discussed. The percentage weight of shoulder girdle's muscle to live weight increased conspicuously in WC and WL, but that of brachial and antebrachial muscles was more increased in RIR than in other breeds. The percentage weight of shoulder girdle's muscle to total muscle weight increased in WL females and did not change in males of WC and WL and in females of BPR and RIR. It seemed that shoulder girdle's muscle developed slightly larger than other subparts' in forelimb.