Large（394.5 - 401.8 g）, middle（283.8 - 324.3 g）and small（94.5- 112.3 g） flounder（ Paralichthys olivaceus ）juveniles were stocked into 8 tanks of each 10.0 m ? 10.0 m ?0.8 m and fed the diets containing Chinese herbs including Lonicera japonica Thumb, ginseng root, and hawthorn at a water temperatures of 16 - 22℃ for 28,56 and 83 days, respectively. The results showed that the large, middle and small fish fed the diet containing Chinese herbs had significantly 22.4 %, 18.9 % and 2.9 % （ P 〈 0.05） higher specific growth rate, 3.0% - 36.4% ,23.53% and 11 . 1% （ P 〈 0.05） higher feed conversion efficiency and 20.77 % , 4.26 % - 39.42 % and 12. 14 % lower feed conversion ratios than the control fish, respectively. There were 11.66% , 13.49% and 9. 13% higher pepsin activities in the stomach and 11.3%, 16.64% and 8.55% higher proteinase activities（ P 〈 0.05） in the intestines in the large, middle and small fish fed the diets containing Chinese herbs than those in the same size fish in the control, respectively. For the amylase activities, however, there were no significant differences among the treatment groups（ P 〉 0.05）. The superoxide dismutase （SOD）activities were 9.53%, 9.09% and 15.14% （ P 〈 0.05） higher in the large, middle and small fish fed the diet containing Chinese herbs than those in the same size fish in the control, respectively, while the lysozyme activity and total protein contents were found not significantly different in the serum among the experimental groups.