The performance of two fat-tailed sheep breeds, Chaal and Zandi, and their F1 and R1 crossbred lambsfrom a lean-tailed breed, Zel, was compared. The weaned lambs from the Chaal and Zandi groups were finished over periods of 105 and 90 days, respectively, and body weight gain and feed consumption were recorded. Forty six male and female lambs from the six finishing groups were slaughtered. The weights of blood, internal organs, intestines before and after removal of digesta, head, feet, pelt and carcasses were recorded. The left sides of the carcasses were cut into six pieces. Individual joints were dissected into lean meat, bone, subcutaneous fat (SCF), intramuscular fat (IMF) and trimmings, and weighed separately. The fat surrounding the intestine and kidney was weighed and considered as internal fat. All the soft tissue (lean meat and fat) of the left sides of the carcasses was ground and representative samples were taken for chemical analyses. The differences of eye muscle (Longissimus dorsi) area (cm2), and protein and bone percentages were not significant between both breeds and their crosses. In the R1 the fat-tail percentage was less than in the F1 and pure lambs of both breeds. In contrast, the SCF and IMF percentages were higher in all crossbred combinations. The internal fat percentages in crossbreds were higher, and in the Chaal group differed significantly from that of the pure lambs. The SCF/IMF ratio in the R1 lambs was lower than in the pure breds. This difference for Chaal crossbreds was significant. The lower ratio of SCF/IMF and the higher internal fat of crossbred lambs compared to pure breds showed that carcass quality of the crossbred was inferior compared to the pure bred lambs in terms of fat distribution in the body.