This study was framed to investigate the ⁶⁰Co gamma radiation induced morphological and histologicalvariations in freshwater prawn Macrobrachium rosenbergii. The LD₅₀ value of ⁶⁰Co gamma irradiated M.rosenbergii observed (by probit analysis) at 30 Gy. Prawns were irradiated to four different dose levels(3 mGy, 30 mGy, 300 mGy and 3000 mGy) using Theratron Phoenix TeleCobalt Unit [P-33] and one con-trol group (without irradiation) maintained separately. Irradiated groups exhibited several morphologicalvariations such as discoloration; damaged rostrum; opaque coloration in cephalothorax; black bands anddot formation in abdomen; deformed uropods and telson in tail regions when compared with controlgroup. The Hepato Somatic Index reflected the severity of radiation on hepatopancreas. Histological vari-ations in gills, hepatopancreas and muscles of irradiated groups were observed. In gills, structural changessuch as swollen and fused lamellae, abnormal gill tips, hyperplasic, necrotic and clavate-globate lamellaewere observed in gamma irradiated prawns. Accumulation of hemocytes in hemocoelic space, interstitialsinuses filled with abnormal infiltrated hemocytes, the tubular epithelium with ruptured basal laminae,abnormal and coagulated lumen, necrotic tubules, thickened basal laminae, tissue debris, necrotic hepa-tocytes were observed in irradiated prawn hepatopancreas. In muscle, shrinkage of muscular fiber andnecrotic musculature were observed in irradiated prawns. These structural alterations of the organs itis felt could affect the vital physiological functions such as respiration, osmotic and ionic regulation ingills and muscles; absorption, storage and secretion of the hepatopancreas which in turn could adverselyaffect the growth and survival of freshwater prawn M. rosenbergii.