Abstract: In order to examine the effect of supplementing chitosan and probiotics in the diet on the growth of juvenile fish Fugu obscurus(initial weigh of 3.15 ± 0.05g and initial length of 4.00 ± 0.27cm),different levels of chitosan(0.0 %,0.2 %,0.5 %,1.0 % ),probiotics(0.0 %,0.1 %,0.2 %,0.4 % ),the complexof chitosan and probiotics,mannan oligosaccharide and probiotics were tested in a 82week trial1Each diet was fed to triplicate groups twice daily1Body weight,body length,hepatomatic index,protease and amylase in the intestine and hepatopancreas,RNA/DNA ratio in white muscle were measured1The results showed that weight gain rate(WGR)of the control group was 476.4 % and the length gain rate(LGR)was 87.3 % 1The WGRs of fish fed with chitosan at level of 0.2 % or probiotics at level of 0.1 % in the diet were significantly higher than those in other groups1No significant difference was observed on LGR in all supplementation groups1The contents of protein and lipid in the white muscle of the control were 82.94 % and 11.21 %,respectively1All the tested additives supplemented to the basal diet could markedly reduce lipid content and increase protein content in the white muscle,decrease the weight of hepatomatic index1The study also indicated no significant difference on protease activity in the intestine and hepatopancreas while significant higher amylase activity in the intestine in both 0.2 % chitosan and 0.1 % probiotics supplementation groups,as well as RNA/DNA ratio in white muscle(P <0.05)1It can be concluded that chitosanor probiotics could promote growthof the fish by enhancing intestine amylase and protein synthesis