Comparative study of esterases polymorphism were studied in Macrobrachium rosenbergi and Penaeus indicus of two prawns belonging to fresh water and marine water respectively, Six tissues were studied viz; Gill, Hepatopancreas, Intestine, Muscle, Brain, and Eye. ER esterases are noticed in Gill, of both marine and fresh water prawns. CE esterases are noticed in all the tissues in fresh water and marine water prawns. CHsp esterases are present in intestine of both the prawns. But Esdp, ArE, ESE esterases are noticed in marine prawns only i.e. P. indicus where as in fresh water prawns this type of esterases are completely absent.