Abstract: The experiment was undertaken to comparatively study muscle chemical composition of crossbred male lambs of Poll Dorset × Small Tail Han Sheep at ages of 7-and 13-month-old. Five 7-and 13-month-old male lambs，selected from the flocks raised in intensive production system，were slaughtered. Longissimus dorsi (LD) was sampled and muscle chemical composition was determined. The results showed that there was no significant difference in the contents of dry matter，crude protein，crude fat，ash，calcium，and phosphorus in LD between 7-and 13-month-old male lambs (P>0.05). The contents of glutanmic acid，threonine，leucine in LD of 7-month-old male lambs was markedly higher than that of 13-month-old male lambs(P<0.05)，but histidine was lower. There was no significant difference in the contents of the other amino acids，total essential amino acids，total non-essential amino acids，and total amino acids. The content of linoleic acid in LD of 7-month-old male lambs was higher about 45% than that of 13-month-old male lambs. There was no significant difference in the contents of the other fatty acids，fatty acids，total unsaturated fatty acids，total unsaturated fatty acids to total saturated fatty acids ratio(P>0.05). The contents of Mg，Zn，Cu，and Mn in LD of 13-month-old male lambs showed increasing tendency，and iron was increased by 17.2% (P>0.05) compared with 7-month-old male lambs. The present study indicated that the nutritional value of Longissimus dorsi was the same between 7-and 13-month-old male lambs.

Key words: intensive production system; lamb; age; muscle; chemical composition