Heavy metal pollution is one of the main anthropogenic pollutions causing serious and long lasting damage to all living organisms. The effect of nickel chloride on protein and amino acid contents of liver, kidney and brain of freshwater fish, Labeo rohita have been studied. The fish were exposed to sublethal concentration of nickel chloride 1/5th (high), 1/10th (medium) and 1/15th (low) of the 96 hour LC50 for the period of 10 and 20 days. All the sublethal concentration of nickel chloride exposed fish for the period of 10 and 20 days showed decrease the protein and increase the amino acid content in liver, kidney and brain of Labeo rohita. The significant alterations showed toxic effect of heavy metal nickel chloride at biochemical levels.