The requirements of carp and rainbow trout for essential amino acids (EAA) were determined based on the daily increase of each EAA in the body of these fish species when they EAA increased daily in 100g of the body weight correspond aqqrpximately to the requirements for EAA of these fish species pre 100g of the body weigh per day, these amounts of EAA should be supplied from the dietary proteins. It was found that there were no distinct differences in the EAA requirements between carp and rainbow trout. The comtents of EAA in the dietary proteins (%) needed to satisfy the requirements of carp and rainbow trout were; leucine, 4.1, 4.4, isoleucine, 2.3, 2.4, valine, 2.9, 3.1, threonine, 3.3, 3.4, phenylalanine, 2.9, 3.1, tyrosine, 2.0, 2.1, methionine, 1.6, 1.8, cystine, 0.8, 0.9, tryptophan, 0.6 0.5, arginine, 3.8, 3.5, histidine, 1.4, 1.6, and lysine, 5.3 and 5.3, respectively, when diets containing 40% protein of an 80% digestibility were supplied at a feeding rate of 3% of the weight.