Prawns have been contributing almost 15% by value in global aquaculture production. In this study, different size groups (4-19 cm) of fresh water prawn, Macrobrachium malcolmsonii (Milne-Edwards, 1844) (Decapoda: Palaemonidae) were collected from the Cauvery River, Tamil Nadu, India, and estimated to identify the protein (P), lipid (L) and carbohydrate (CHO) level. The adult prawns exhibited highest values 61.63% P, 6.95% L and 5.40% CHO. The gas chromatography of small size groups of prawns showed increased amount in various fatty acids such as palmitic acid, stearic acid etc. The tissues result determined by high performance liquid chromatography showed that the amino acids such as Aspartic acid, Lysine etc., are high in adult groups. The protein profile of the muscle samples displayed various polypeptides ranging from 200 to 20 kDa. Results of this study clearly implied the biochemical and nutritional constituents of freshwater prawn, M. malcolmsonii. It would be useful to design the required composition of feed in order to get higher yield at lower cost production.