This study investigated the effects of dietary supplementation with rosemary complex powder on the growth performance of native chickens. In total, 180 one day-old native chicks were assigned to one of three dietary groups (60 birds each). The control group (Group A) received the basal diet. In addition to the basal diet, the two experimental diets (Groups B and C) were supplemented with 0.2% and 0.4% rosemary complex powder, which contained rosemary leaves, sweet basil, pineapple sage and sweet lavender. Over 19 weeks, feed intake was recorded to determine the average daily gain and feed conversion ratio. In weeks 10 and 15, blood samples were taken for serum antibody titer analysis. At the end of the experiment, serum immunoglobulin A (IgA) and serum immunoglobulin G (IgG) concentrations were examined. No differences were observed among the groups in terms of the starting weight, weight in week 19, average daily feed intake, average daily gain, or average feed conversion ratio. The addition of rosemary complex powder improved total weight gain by 1.52%. Serum IgA and serum IgG concentrations were significantly lower in the experimental groups in comparison to the control group (p<0.05). Villus height, villus width, crypt depth, and villus height/ crypt depth ratio were significantly higher in group B than in group A (p<0.05). In summary, rosemary complex powder improved the intestinal absorption capacity of chickens and significantly reduced their immunoglobulin concentrations.