This study evaluated the optimum inclusion of a feed oil additive chemically extracted from cashew nuts in lamb diets on the physicochemical and sensory attributes of burgers produced from their meat. Forty lambs (26 ± 2.4 kg of initial BW and 5 months of age) were used in a block randomized design with ten experimental units per treatment. Lambs were fed a total mixed ration containing cashew nut shell liquid (tCNSL) at levels of 0, 7.5, 15 and 22.5 g/kg g/kg of dietary dry matter. Lambs were slaughtered, and the meat was processed for burger production. The addition of tCNSL to the diets promoted a quadratic increase in DMI (P = 0.034), ADG (P = 0.016) and slaughter BW (P = 0.002). However, the addition of tCNSL to the lamb diet did not change (P >0.05) the concentrations of moisture, protein, lipids, crude ash and cooking losses; water holding capacity or hardness and color index a* of the lamb meat burgers. There was a linear decrease (P <0.001) with lower formations of peroxides and metomyoglobins in lamb meat burger when dietary levels 15 and 22.5 g/kg of tCNSL were added in diets. The pH of the lamb meat burgers increased linearly (P = 0.0196), due to the inclusion of tCNSL in the lamb diets. The L* color index reduced linearly (P = 0.0179) while b* and C* color increased linearly (P ≤ 0.05) with the addition of tCNSL in the diet. The inclusion of tCNSL did not change (P > 0.05) in the sensory attributes of the lamb meat burgers. All variables scored between 7 and 8, being considered by the tasters as moderately liked and very liked, obtaining a good overall acceptance. However, the preference (P = 0.042) ranking of the panellists was for burgers from the meat of lambs fed with tCNSL, regardless of the level of inclusion, compared to treatment without tCNSL. It is recommended to include up to 15 g tCNSL/kg DM as antioxidant in the lamb’s diet because it improves growth performance, color index and physical quality, and reduces the elasticity, chewability, lipid peroxidation and metmyoglobins, and increasing the preference of lamb meat burgers.