This study was conducted to evaluate the effect of rosemary leaves meal as a natural antioxidant in broiler diet on growth performance, blood parameters and the immune response of broiler chickens. A total of 150 Cobb chicks were assigned equally into five treatment groups. The chicks were fed the same basal diet and were submitted to the following dietary treatments:  the first group fed a basal diet (control), while the other four groups were fed basal diet supplemented with 0.25, 0.5, 0.75 and 1.0 % of rosemary leaves meal. Chicks fed diet with 0.25% rosemary leaves meal had significantly (P<0.05) greater production performance than the control group. Feed intake and total cost were significantly decreased in chickens fed diet with 0.25% and 0.5% rosemary leaves meal than those fed diet with, 0.75 and 1.0 % of rosemary leaves meal and control group. Rosemary leaves meal had significantly improved the digestibility of crude protein and Ash. Feeding diet with rosemary leaves meal significantly decreased serum urea, creatinine, alanine amino transferase, triglycerides, cholesterol, high-density lipoprotein (HDL) and low-density lipoprotein (LDL) while increased glucose, total protein, triiodothyronine, thyroxine, glutathione, hemoglobin, packed cell volume, red blood cell, white blood cell, lymphocyte, monocytes, mean corpuscular hemoglobin concentration (MCHC), globulin, globulin-γ, bactriocide activity, lymphocyte transformation test (LTT), immunoglobulins (IgY, IgM and IgA), interferon-gamma (IFNγ), interleukin-2 (IL2),  interleukin-10 (IL10), phagocytic activity and index compared to control group. Therefore, rosemary leaves meal at 0.25% could be considered as a natural antioxidant in broiler diet, potential growth promoter and immune stimulant for poultry.