An experiment was conducted to determine the effects of unsaturated fatty acids supplementation on growth performance and carcass characteristics of finishing lambs. Thirty-two finishing Afshari lambs (initial weigh 58 ± 5 kg and 8 mo age) were used in a completely randomized design with 4 treatments (slaughtered in time series) and 8 lambs/treatment for the final 30 d before slaughter. The slaughter times were d 0 (first day after adaptation period), 10, 20 and 30 after beginning of experiment. The lambs individually fed to the basal diet (80% concentrate; 65% barley grain and 11% soybean meal and 4% mineral and vitamin supplement, and 20% alfalfa hay) and daily fed with 60 g sunflower oil and 40 g fish oil. Body weight changes and daily feed intake were recorded. Blood samples, ultrasonography (back fat and Longissimus muscle thickness) and rumen fluid was taken on the last day of each periods. Cold and warm slaughter weight, dressing percentage, fat yield, pH, moisture loss, chemical composition, and visceral organs mass were measured. The results of this study were revealed that body weight, back fat and Longissimus muscle thickness, for d 0, 10, 20 and 30 after allocating to high oil supplemented diets was 59.20, 62.45, 65.26, and 69.07 kg; 4.8, 5.09, 5.36, and 4.79 mm; 24.41, 24.28, 25.90, and 30.38 mm; respectively. Warm and cold carcass weight and rumino-reticlum mass increased during time. Oil supplementation decreased tail weight to carcass weight ratio from 0.17 to 0.12 and also improved feed conversion ratio. Plasma concentration of cholesterol was highly increased by oil supplementation and was significantly different among the experimental diets (P < 0.01). This experiment showed that short-term inclusion of mixed fish and sunflower oils in final days of finishing lambs diet can improve carcass characteristics and performance of lambs.