Cobalt (Co) is one of the essential elements for fish, with various biological functions, including in growth promotion, blood production, reproduction, and immunity. In this study, we evaluated the effects of dietary cobalt methionine (CoMet) on growth performance, mineral deposition, and hepatic enzyme activities in the juvenile pearl gentian grouper ( ♀). Six extruded isonitrogenous and isoenergetic diets (51% crude protein and 13% crude lipid) were formulated by supplementing the basal diet with CoMet, providing actual Co contents of 0.30, 1.75, 3.42, 6.73, 12.56, or 25.50 mg/kg diet, which were fed to groups designated D1, D2, D3, D4, D5, and D6, respectively. Each diet was randomly assigned to triplicate groups of 20 juveniles (initial weight, 60.02±0.42 g). The experiment was conducted for 8 weeks in plastic cylindrical tanks in an indoor recirculated feeding system. The weight gain rate (WGR) and specific growth rate (SGR) of the juveniles both increased and then decreased with higher CoMet levels, and both were significantly higher in the D3 group than in the other groups ( < 0.05). The feed conversion rate declined with dietary CoMet level decrease but increased with dietatry CoMet increase, and the lowest feed conversion rate was observed in the D3 group. There were no significant differences in the moisture or ash contents of the muscle among the treatment groups ( > 0.05). The crude protein content of the muscle was clearly reduced by dietary CoMet, and was significantly lower in the D5 and D6 groups than in the other groups ( > 0.05). The muscle of fish fed the D6 diet had the highest crude lipid content ( < 0.05), and the muscle of fish fed the D4 diet had the lowest crude lipid content ( < 0.05). The Co contents of the liver, intestine, vertebrae, and muscle were significantly increased with CoMet supplementation ( < 0.05). The Co deposition rate in the whole body was markedly increased (from 0.30 mg/kg to 6.73 mg/kg diet) by dietary Co ( < 0.05), and then plateaued in the fish fed diets with Co contents of 12.56 mg/kg (D5) and 25.50 mg/kg (D6). The Fe, Cu, and Zn contents of the liver increased from group D1 to group D3 and then declined from group D4 to group D6 ( < 0.05). The Mn content of the liver was significantly reduced by dietary CoMet ( < 0.05). The glutathione peroxidase activity of the liver increased and then decreased as CoMet increased ( < 0.05). Fish fed the D5 or D6 diet showed significantly lower hepatic malondialdehyde contents ( < 0.05). The arginase activity in the liver was significantly increased by dietary CoMet ( < 0.05). The carboxypeptidase A activities in the livers of the D4, D5 and D6 groups were significantly higher than those in the D1, D2 and D3 groups ( > 0.05). In conclusion, under the experimental conditions used here, the optimum Co requirement for the juvenile pearl gentian grouper was 3.25 mg/kg diet (53.28 mg CoMet/kg diet) based on a broken-line regression of SGR.