The aim of this study was to evaluate the effect of rosemary herb on performance, egg quality, blood profile, immune function and antioxidant status in Hi-sex Brown laying hens. A total of 96 thirty-six-week-old laying hens were assigned to 4 dietary treatments (6 replications of 4 hens per group) and were fed the control diet or diets supplemented with 3, 6 or 9 g·kg^–1 of rosemary powder until 52 weeks of age. There were no differences in live body weight, feed consumption, feed conversion ratio or egg weight due to adding rosemary. Egg numbers and egg mass linearly increased with rosemary supplementation. Adding rosemary to laying hen diets resulted in a linear increase in yolk percent (P < 0.05)and yolk-to-albumen ratio (P = 0.01), and a decrease in albumen percent (P < 0.05)compared with the non-supplemented group. Serum constituents were not significantly influenced by rosemary, except urea, total cholesterol, immunoglobulins M (IgM) and A (IgA) concentrations. In comparison with the control group, the diet enriched with rosemary numerically reduced serum triglycerides, cholesterol and LDL-cholesterol concentrations, but HDL-cholesterol level was elevated with the same addition. Superoxide dismutase activity was linearly and quadratically (P = 0.007 and 0.002, respectively) increased in rosemary groups, and was maximized (290 U·ml^–1) at 6 g·kg^–1 diet. In conclusion, rosemary supplemented up to 6 g·kg^–1 diet can be used as effective feed additive to improve performance, immunity and antioxidant status in laying hens.