In this study, 45 weaned Kivircik male lambs with an average initial body weight [BW] of 26.23 kg were randomly assigned to five experimental groups (G10, G, G12, G16, G18J fed 10, 12, 14, 16, 18 % crude protein (CP), respectively. It was observed that G 16 had higher BW than the first three groups (p<0.05), but there were no significant differences between G16 and G18. G16 had higher daily body weight gain [BWG] than other groups. During the study, when compared with first three groups, G16 had significantly higher BWG (p<0.05), but no significant difference was observed between G16 and G18. The lowest DMI was observed in G10 (p<0.05), however, there were no differences between G 14, G16 and G18. The best and the lowest feed efficiency were observed in G16 and G10, respectively. When the analysis results of faeces samples were compared, the lowest nitrogen (N) excretion was detected in G10 and G12, and the highest N excretion was detected in G18 (p<0.05). However, there were no significant differences between G14 and G16. Percentages of N digestibilities of G16 and G18 were higher than those of other groups (p<0.05). There were no significant differences between G16 and G18, and between G10, G16 and G14. The analysis results of serum samples obtained from experimental groups showed that, except for serum urea and albumin levels, there were no significant differences between the level of other metabolites. G 10 had lowest serum albumin level (p<0.05), and there were no significant differences between the other groups. Serum urea levels of G 14, G16, G18 were similar and higherthan those of G10 and G12 (p <0.05). The lowest serum urea level was determined in G10 (p<0.05). Consequently, when it was considered that feeding Kivircik lambs with higher protein level than 16 % had no advantage for performance and would be cause of economic loss, it can be said that 16% CP was optimal.