Description: The aim of this experiment was to investigate the effect of dietary crude protein (CP) level on serum immunonoglobulin G (IgG) and the performance in male lambs. Twenty Kivircik male lambs were randomly selected for this experiment. Ages ranged between 120-135 days and average body weight was 29.01с3.65 kg. Ten lambs were randomly assigned to each of the two experimental diets containing 10 CP and 18 CP respectively, to determine the effects of dietary CP level on performance and serum IgG. Live body weights and daily body weight gains were greater (P<0.05) for lambs fed the 18 CP diet compared to lambs fed 10 CP diet on days 30 and 60. Body weights for lambs fed 10 CP and 18 CP were 33.36 с 1.53 kg and 38.63 с 1.74 kg (day 30), and 37.20 с 1.30 kg and 43.05 с 1.05 kg (day 60); respectively. Cumulative feed intakes of groups were similar. Serum IgG values of lambs fed 10 CP (2.79 с 0.31 mg/ml) were higher (P< 0.05) than those in the other group (1.98 с 0.17 mg/ml) on day 0. Differences between serum IgG values on day 30 and 60 were not statistically significant.