ABSTRACT The aim of this study was to evaluate the effects of copaiba oleoresin (CO) as a substitute for sodium lasalocid on the carcass characteristics and meat quality of feedlot lambs fed a high-concentrate diet. Twenty-four Pantaneiro lambs, aged 152 days and weighing an initial body weight of 21.2 ± 3.9 kg, were distributed in a randomised block design with three treatments and eight replications. The treatments correspond to the additive supplements: LAS (22.5 mg of sodium lasalocid/kg of diet); CO-0.5 (0.5 mL of CO/animal/day); CO-1.0 (1.0 mL of CO/animal/day). The doses of CO were administered to the animals orally with the aid of a graduated syringe. Lambs supplemented with LAS had higher hot carcass weight, cold carcass weight, cold carcass yield, and degree of fattening compared to CO-0.5, while CO-1.0 did not differ from LAS. It can be concluded that daily ingestion of CO up to 1.0 mL/lamb did not negatively affect carcass characteristics when compared to LAS supplementation. However, lower ingestion (0.5 mL/day) can reduce the carcass weight and carcass yield. Although CO supplementation minimally affected the meat quality and FA profiles, both doses reduced crude protein content in meat.