An experiment was conducted to investigate the effect of dietary organic and inorganic copper sources on broiler’s performance, immune responses and blood parameters. In this experiment 420 Ross 308 broiler chicks (male) were randomly assigned into the 7 treatments with 4 replicates (15 birds per each replicate) based on completely randomized design. Copper at the rates of 8, 16 and 32 mg/kg and in the forms of organic (copper-methionine (Cu-Met) chelate) and inorganic (copper sulfate pentahydrate) was added to the control diet. The dietary treatments were offered from 7 to 42 day of age. At the age of 10 days, birds received Newcastle disease vaccine orally. 6 and 12 days later, blood samples were collected from the wing vein of two birds per replicate. Serum antibody titers against Newcastle virus were determined by beta HI test and expressed as log 2 . Also, at 28 and 35 days of age, two birds from each pen were immunized intraperitoneally with 0.5 ml of 10% SRBC (Sheep Red Blood Cell) suspension to determine primary and secondary humoral antibody responses. 7 days after each injection, blood samples were collected from the birds to evaluate antibody titers against SRBC. Total antibody titers to SRBC were determined by agglutination with routine procedure . Antibody titers were expressed as the log 2 of the reciprocal of the highest plasma dilution giving complete agglutination. At 22 and 42 days, blood samples were collected to investigate serum total cholesterol, HDL cholesterol and TG concentrations. ource of copper had no effect on feed consumption, weight gain, feed conversion ratios, and accumulation of Cu in the liver, however inorganic source of Cu at the level of 32 mg/kg reduced Fe and Zn content of the liver compared with the control ( P 0.05). The serum high-density lipoprotein and total cholesterol contents remained unchanged, however serum triacylglycerol content reduced in chicks supplemented with organic (at the levels of 16 and 32 mg/kg) and inorganic (at the level of 32 mg/kg) sources of Cu compared with control ( P 0.05). Although spleen and liver weights were not affected by dietary treatments, compared to control bursa weight increased in chicks supplemented by organic source of Cu at the levels of 16 and 32 mg/kg ( P 0.05). Supplementing organic form of Cu (32 mg/kg; P 0.05) reduced the heart weight compared with control. Source of Cu had no effect on anti-body titers against Newcastle Disease Virus but SRBC titer increased by organic source of Cu (both levels of 16 and 32 mg/kg), significantly. Results indicated that source of Cu did not influence growth performance, but using organic source of Cu may be effective in reducing serum triacylglycerol and improve immune responses