The current study was conducted to investigate the dietary effects of various amounts of Zataria multiflora seed powder on hematological, biochemical and immunological parameters in broiler and native chicken, in a random study using 4 treatments including 0 (control), 100, 200 and 300 mg/kg of Z. multiflora powder in diet for 42 days. At the end point, blood specimens were taken from wing vein and after the preparation of the serum samples, the following biochemical factors were measured using standard assay kits: total protein, albumin, globulin, triglyceride, cholesterol, high density lipoprotein and low density lipoprotein as well as hepatic enzymes activates including, aspartate aminotransferase, alanine transaminase and gamma-glutamyltransferase. The number of lymphocytes and heterophiles also were counted. Furthermore, immunoglobulin contents were measured in serum samples. The obtained results showed that the herbal supplement can significantly alter all of the aforementioned factors in both races compared to the control. In addition, racial differences of the parameters including cholesterol, triglyceride, LDL, lymphocytes, heterophiles, ALT activity and IgM were recorded in control groups. Conclusively, supplementation with Z. multiflora powder can improve hematological and biochemical parameters in both races. However, the immunoglobulin contents did not change remarkably and seems like the higher amounts of the herbal powder should be used to improve immunological responses.