The effects of dietary cobalt dichloride on survival, growth performance, haematological parameters, antioxidases activities, digestive enzymes activities, V_B12 contents in serum and liver, tissue cobalt residues, and intestinal and liver morphology of turbot (Scophthalmus maximus L.) were studied for safe utilization of cobalt dichloride in fish feed. The experimental dietary cobalt dichloride inclusion level was 0, 8, 40 and 80 mg/kg respectively. Six replicates of 30 fish were used for each treatment group. No mortality was observed during the 10-week feeding trial. Growth performances of fish were not significantly affected by dietary cobalt dichloride supplementation from 0 to 40 mg/kg (P>0.05), however, 80 mg/kg dietary cobalt dichloride significantly decreased the final weight, specific growth rate, final weight, feed intake, hepatosomatic index, and viscerosomatic index (P<0.05). Supplementation of 40 and 80 mg/kg cobalt dichloride in diet decreased activities of catalase, aspartate transferase, and alkaline phosphatase in fish (P<0.05). The activity of stomach amylase was significantly decreased by dietary supplementation of 40 and 80 mg/kg cobalt dichloride (P<0.05), while dietary supplementation of 40 mg/kg cobalt dichloride significantly decreased the activity of trypsin (P<0.05). With increasing level of dietary cobalt dichloride, the glucose and V_B12 content in serum and liver and the cobalt residue in liver and muscle increased significantly (P<0.05). No lesion or damage was found in intestinal structures of fish from all treatments. However, 40 and 80 mg/kg dietary cobalt dichloride impaired the liver tissue and widened the hepatic sinusoid. The present results proved that 8 mg/kg cobalt dichloride was safe as additive in fish feed.