The metal works industries release a good amount of heavy metals like mercury, cadmium, manganese, nickel and chromium which ultimately fall in the water bodies. Heavy metals are known to cause alterations in various tissues of fish at the biochemical level. Cadmium is an extremely toxic heavy metal which is widely used in mining, metallurgical operation, electroplating industries manufacturing vinyl plastics, electrical contacts, metallic and plastic pipes. Effluents from such plants are sources of cadmium into aquatic environments. Hence an attempt was made to study the impact of sublethal concentration of cadmium chloride on the protein and amino acid content changes in gill, liver and kidney of the freshwater exotic fish, Hypopthalmichthys molitrix. As the period of exposure to sublethal concentration of cadmium chloride has considerable influence on the metabolic changes the study was made at 7, 14 and 21 days. The protein and amino acid levels changes in gill, liver and kidney were estimated in control and experimental fishes. Significant elevation of amino acid whereas protein level decreased in gill, liver and kidney of fish treated with sublethal concentration of cadmium chloride when compared with control fish. But the maximum decrease of protein and elevation of amino acid contents were observed in all tissues at 21 days. These results suggest that the cadmium chloride causes deleterious effects on protein metabolism. Key words: Hypopthalmichthys molitrix, cadmium chloride, protein metabolism, gill, liver, kidney