In lamb production, deciding the optimal slaughter weight (SW) has great importance on product quality. The aim of the study was to determine the optimum SW for lambs from a thin-tailed breed (Kivircik) and a fat-tailed breed (Kangal Akkaraman) in order to get high-quality meat and carcass. Kivircik (n=60) and Kangal Akkaraman (n=59) lambs were allotted to five SW groups (20, 28, 36, 44 and 52 kg). In Kivircik lambs, backfat thickness and fatness score gradually increased in parallel with the increase in SW, while the increase in the tail fat and kidney knob and channel fat (KKCF) proportions were observed by up to 36 kg. In Kangal Akkaraman lambs, evident increases in fatness parameters, except tail fat proportion, were observed when the SW increased from 44 kg to 52 kg. Meat pH, Warner Bratzler shear force (WBSF) and cooking loss values were not influenced by SW in lambs of both breeds. As SW increased in Kivircik lambs, there was a significant decrease in meat lightness and an increase in yellowness. In Kangal Akkaraman breed, lambs slaughtered at 20 kg and 28 kg had higher L* values, and lower a* and C* values than those of other SW groups. In Kivircik lambs, the total PUFA proportion and the ΣPUFA/ ΣSFA ratio were lower in SW-44 and SW-52 groups than those of SW-20 and SW-28 groups. Decreases of these parameters were in SW-52 group in Kangal Akkaraman lambs. In meat samples of both breeds, SW-52 groups had a lower Σ