The present study was conducted with 288 one-day-old mixed broiler chicks (Ross 308) to investigate the effects of dietary supplementation with various levels of turmeric powder on blood constituents and antioxidant activity. The chicks were randomly assigned to eight dietary groups, which were given turmeric powder levels of 10, 12, 14, 16, 18 and 20 g/kg feed, and two control groups (positive and negative). Each dietary group contained six replicates with six birds each. The results showed that the concentrations of glucose, albumin, blood urea nitrogen and total bilirubin, and the enzyme activity of alanine aminotransferase decreased significantly in the serum of broiler chickens treated with turmeric powder compared with untreated chickens (control groups). However, there was no significant reduction in the concentration of serum creatinine or the enzyme activities of aspartate aminotransferase, alkaline phosphatase, lactate dehydrogenase and creatine kinase in serum. The activity of the gamma-glutamyl transferase enzyme did not change either. There was no significant increase in the concentrations of serum total protein and globulin in the groups treated with turmeric powder compared with control groups, except at weeks 2 and 4. The total antioxidant capacity in tissues (liver, heart and kidney) and serum was not affected significantly by turmeric powder. From these results it can be concluded that dietary turmeric powder had positive effects on the blood biochemistry parameters of broiler chickens, but that antioxidant activity was not improved.