The aim of this study was to investigate the effects of peppermint supplementation on growth performance and some immune parameters in the Caspian Roach (R. caspicus). A total of 540 specimens (2.4±0.12 g) were allocated into 12 tanks and triplicate groups were fed with diets containing 0, 2, 3 and 4 g/kg peppermint powder for 60 days. At the end of the trial, parameters including growth performance, epidermal mucus protein level, alkaline phosphatase as well as lysozyme activity were measured. The results showed that body weight gain and specific growth rate of fish fed with diets containing peppermint increased significantly. While, the feed conversion ratio in fish treated with peppermint decreased significantly compared with the control group. Additionally skin mucus protein levels, alkalin phosphatas and lysozyme activity increased significantly compared to control group. These results indicated that peppermint as dietary supplement affects the growth performance and immune parameters of the Caspian roach beneficially.