Terminal sire mating and supplementation were used to improve growth rate and muscling in hair sheep breeds. However, their effect on the fatty acid profile of different fat depots in lambs has not been reported. Forty-seven lambs (5-mo old), 23 purebred hair sheep (Barbados Blackbelly or BB, BW = 16.2 ± 1.9 kg; St.Croix or SC, BW = 19.5 ± 2.0 kg) and 24 crossbred wool (Dorset, D) x hair (BB; BW = 21.7 ± 2.3 kg or SC; BW = 21.7 ± 2.9 kg) of both sexes were rotationally grazed on predominately tall fescue with or without soy hull supplementation during summer. Soy hull was provided at 2.0% of BW at individual feeding stations. After 90 d of grazing, lambs were harvested, and intramuscular, subcutaneous and kidney fats were obtained from each carcass. Total lipids from each fat depot sample were extracted by the chloroform-methanol method. Extracted lipids were prepared for the fatty acid methyl esters (FAME) and then analyzed by a gas chromatography. All data were analyzed as a completely randomized design with breed type (pure- or cross-bred), supplement (with or without soy hull), and sex (male or female) as main effects. The fatty acid profiles of different fat depots from experimental lambs were significantly influenced by supplementation and sex. Compared with lambs fed supplement, pasture-only fed lambs had higher (P < 0.01) concentrations of linoleic (C18:2n6, 6.83 vs 4.96%), arachidonic (C20:4n6, 4.08 vs 2.27%), docosapentaenoic (C22:5n3, 1.41 vs 0.73%) and docosahexaenoic (C22:6n3, 0.45 vs 0.25%) acids in intramuscular fat; a higher (P < 0.01) concentration of stearic (C18:0, 26.0 vs 22.4%) acid, but lower (P < 0.01) concentrations of C16:0 (19.4 vs 22.2%) and C18:1n9 (31.4 vs 37.2%) in subcutaneous fat; and a higher (P < 0.01) concentration of C18:1n9 (38.7 vs 33.1%), but lower (P < 0.01) concentrations of C18:0 (23.7 vs 29.4%) and C18:2n6 (1.13 vs 1.76%) in kidney fat. The results indicate that fresh lamb from pasture only fed-lambs might have healthier fatty acid profiles compared with that from lambs supplemented with soy hull, regardless of breed types.