The fresh water field crab, Spiralothelphusa hydrodroma is an important human food source in parts of South India and the crab is constantly exposed to pesticides, which are used extensively to control agricultural pests. Evaluation of the toxic effect of cypermethrin on the experimental crab for the LC₅₀ value was carried out. Effect of cypermethrin on the quantitative study of the nutritive value viz., protein, carbohydrate and lipid in ovary, spermatheca, hepatopancreas, muscle, gills, haemolymph, brain, thoracic ganglia and eyestalk was studied. It is concluded that the accumulation of cypermethrin in the hepatopancreas is found to be exponential in an environment of cypermethrin which is commonly used as biocides and fertilizers.