The present study was curried out to investigate the effects of feeding the different levels of crude protein (CP) and threonine (Thr) on performance, egg quality and immune responses of laying hens in a completely randomized design with a factorial arrangement, at a 70-day period. Treatmentincludedthree levelof C(100, 95and 90ercent ofHy-Line W36 commercial guide recommendation)andthree levels ofThr(100, 110and 120ercentofHy-Line W36 commercial guide recommendation ). At this experiment, one hundred eighty Hy-Line W36 commercial laying hens (48 weeks old) were randomly allocated into 9 dietary treatments with 4 replicates of 5 hens in each replicate. Feed and water were provided ad libitum during the experiment. The average daily feed intake, feed conversion ratio, egg production, egg weight and egg mass were evaluated for the first 35 days, the second 35 days and the whole trial period. At the end of first and second periods, egg qualitative traits including Haugh unit, yolk index, yolk color, quality and strengthof egg shell were evaluated. In order to investigate immune response, 2 birds per replicate were administered intramuscular injection with sheep red blood cell (SRBC), twice with 10 days interval, and then blood samples were collected 6 and 12 days after first and second injection, respectively. The blood antibody titer at each 2 times and differential counting of leukocyte subsets, albumin and globulin percent were evaluated at second time. At the end of experiment, jejunum mucosa and relative weight of various body organs were studied. The results of this experiment showed that reduction in dietary CP content or increasing dietaty Thr, at the studied levels had no significant effect on average daily feed consumption, egg production ratio, egg mass, feed conversion ratio, Haugh unit, yolk index, and egg shell quality at each time intervals. At the end of the trial body weight change in different dietery groups was similar. No significant difference was found between dietary treatments in white blood cells numbers, early immune response, jejunum histology and relative weight of liver and spleen. However, 10 % reduction in dietary CP caused the reduced egg weight at each three time intervals ( P 0.05) and increase in yolk color at the end of expriment ( P 0.05). In addition, 20 % increase in dietary Thr level in diet compared to recommended level, caused significant increase in antibody titer against SRBC at secondary immune response ( P 0.05), increase in globulin percent, reduction in albumin percent and ratio of albumin to globulin in blood plasma ( P 0.05). There was a significant interaction between CP and Thr levels on secondary immune response ( P 0.05). The relative weight of pancreas increased as dietary Thr level increased ( P 0.05). In conclusion, the results of this study showed that reduction in dietary CP content at studied levels, at 70 days had no adverse effect on performance, egg qualitative traits, and immune responses of layers. But to gain the highest immune response, more Thr compared to recommended level is required. Keywords: Laying hens, Crude protein, Threonine, Performance, Egg quality, Immune responses.