The present paper deals with the study of relative growth of fresh water prawn Macrobrachium assamensis peninsularis. Experiment was conducted to study the effect of different formulated diets. The experiment diets were prepared with similar ingredient composition with only difference in protein supplement source. The stocked animals were fed with control diet (D₀) and three experimental diets (D₁-D₃). The food was given at 8 am and 4 pm at the rate of 5% of the total biomass. Study was conducted during July 2007- June 2008. The relative per month growth increment was observed maximum in the case of animal fed with diet D₃ followed by animal fed with diet D₂. It was 2.08 mm in male and 1.44 in female for per month increment in length of animal fed with diet D₃ and 0.11 gm in males and 0.073 gm in females for per month increment in weight of the same group of animals. Finally concluded that formulated feed to enhanced the relative growth of both the sexes under laboratory condition.