Abstract: This experiment was conducted to investigate the effect of ionophores monensin and lasalocid on performance and carcass characteristics in fattening Arabi lambs. Thirty fattening male lambs with similar conditions (22.14±0.72 kg body weight) were included in this experiment from day 90 until day 150. Three high concentrate diets containing with 30 ppm monensin (M), 30 ppm lasalocid (L) and none additive (Control = C) were offered to lambs in a completely random design. The Body Live Weight (BLW), Average Daily Gain (ADG), Dry Matter Intake (DMI) and Feed Conversion Ratio (FCR) of lambs were measured two weeks interval until eight weeks. Carcass components were recorded at the end of trial. Total ADG and final BLW of fattening lambs fed the diets containing ionophores were significantly higher (p<0.05) than lambs fed the control diet. DMI of the lambs fed diet containing monensin were significantly lower (p<0.05) than other two groups. The same trend was found for FCR, while the differences was significant (p<0.05) only between M and C group lambs. Carcass characteristics was not affected by treatment (p>0.05), but lambs fed diet containing lasalocid had greater dressing (%) and boneless meat (%). It is concluded that the performance and carcass characteristics were improved in diets containing ionophores.