Growth and changes in the mid-gut cell morphology of Penaeus monodon juveniles were evaluated after feeding for 35 days with semi-purified diets deficient in water-soluble vitamins. Diets were prepared by deleting one vitamin at a time from the vitamin supplement consisting of cyanocobalamine, folic acid, thiamine, riboflavin, pyridoxine, niacin, choline, inositol and ascorbic acid. Controls were the complete vitamin diet (control diet 1) and the no vitamin diet (control diet 2). Growth rate was poorest for treatment without vitamin supplement and the inositol and choline-deficient diets. Enhanced growth was observed in prawns fed with the riboflavin-deficient diet. All treatments except control diet 1 showed histopathological changes in the mid-gut cells. Detachment or destruction of the epithelial cells were observed in most cases but more severely in treatments without vitamin supplement followed by inositol, choline and vitamin C.