Fifteen male Rahmani lambs (8 months in age with an average body weight 30.52 ± 0.21 Kg) were used in this study to evaluate the effect of different protein levels in diets on the performance, nutrient digestibility, blood parameters, ruminal characteristics and carcass traits in addition to economical benefit. Animals were randomly divided into 3 similar groups (5 lambs each). Each group was fed on one of the protein level tested (12, 14.70 & 17% CP) for 90 days. The medium protein's ration (14.7 %) was considered as control. The two different protein levels as treatments (high protein, HP = 17%, low protein, LP= 12%). All diets contained the same digestible energy (3.20 MCal/kg DE / kg diet). There was significant (P<0.05) difference in the feed intake, weight gain and feed conversion between different experimental groups. The apparent digestion coefficients of DM, CP, EE, CF & NFE were significantly (P<0.05) increased with increasing dietary protein levels. There was significant (P<0.05) increase in the total protein, albumin, globulin and urea as the protein level increased. The levels of protein had no significant effect on the pH of the rumen, while ammonia-N concentration and total volatile fatty acids were significantly (P<0.05) increased. There were no significant differences in the carcass characteristics between treated groups. Consequently, it was considered that feeding Rahmani lambs with higher protein level than 14.7% had no advantage for performance and would be cause of economic loss, it can be said that, 14.7% CP was optimal.