Effects of olive cake (OC) supplementation on carcass traits, contractile muscle properties and meat quality of lambs fed indoors or grazing in a Medicago arborea rangeland were studied. Twenty-four weaned male lambs (average body weight 24.3 ± 1.1 kg) were assigned into four treatment groups: indoor without OC, indoor with OC, pasture without OC and pasture with OC. The first two groups of lambs were fed indoor with oat hay ad libitum as based diet. The two others reared on natural rangeland improved by Medicago arborea. One of indoor and pasture groups were supplemented with 280 g/d of OC. All the groups received 400 g of concentrate. The experimental trial lasted about 3 months. Then, lambs were slaughtered at 33 kg. Rangeland lambs had higher ADG. Feeding system (FS) and OC supplementation did not affect (P > 0.05) hot and cold carcass weights and dressing percentage. Lambs fed indoor had the greater commercial dressing percentage (P < 0.01) and the higher meat yield for all cuts except neck and thorax compared to pasture lambs. However, they have lower proportions of high-priced cuts and higher proportion of tail. Lean and bone proportions in the carcass were higher, whereas proportion of fat was lower for pasture lambs than for indoor lambs. Moreover, carcass of lambs fed indoor had a thicker subcutaneous fat (P < 0.001) and greater weights of tail and kidney fat than pasture lambs. OC supplementation did not have any significant effect on carcass fatness, meat yield and tissue composition. Pasture lambs meat had lower (P = 0.05) drip loss than that of lambs fed indoor. However, pH was not modified (P > 0.05). Lambs supplemented with OC had lower ultimate pH (P < 0.05). Muscle of lambs fed indoor contained higher proportion of fibres type I (11.5 vs. 7%). However, OC supplementation tended to increase the lactate dehydrogenase activity and to decrease the isocitrate dehydogenase activity (P < 0.10). Total and insoluble collagen contents were similar between groups. Tenderness, juiciness, fat degree and flavour intensity of meat were higher when feeding lambs on pasture. OC supplementation increased only meat juiciness (P < 0.05). In conclusion, feeding lambs on rangeland decreased the carcass fatness and improved meat sensory effects. OC supplementation had little effect on carcass and meat of lambs fed indoor or reared on improved rangeland.