Cobalt (Co) is an essential mineral required in trace quantity in fish diet. Co is extremely scarce in the freshwater resources. Therefore, freshwater fish require a supplement of Co in the diet. The present study was conducted to determine optimum level of Co which could be used as supplement in the diet to enhance the growth of Cyprinus carpio without constituting metal burden to the fish and to work out relationship between accumulation of Co in fish tissues and diet. Also to evaluate the effects of dietary cobalt levels on growth, nutrient deposition and digestive enzyme activities in common carp.