An experiment on requirtment of phosphorus in the dietary ofgrass carp Ctenopharyngodon idellus was catrried out. By the use of casein-gelatin asbasic diet with mono calcium phosphorus as source of phouphorus, the gradientmethod was applied. The results of the experiment demonstrated that the dietaryphosphorus played a great effect on the growth of grass carp. The deficiency ofphosphorus in the diet would cause a slow growth of the fish and high expense offood. By analysing, the whole fish body contains a lower level of water, ash, calcium,phosphorus and Ca/P ratio, but high content of fat with low phosphorus in vertebrae.The over-high phosphorus, however, would also result in slow growth of the fishand even lead to mortality. Thus judging from the growth rate and food consumptionof the fish, the appropriate value of phosphorus in the grass carp diet should be0.95--1.10% and the requirement of available phosphorus in the diet of grass carp is 0.85--1 .00%. The experiment indicated that phosphorus should be the principalmineral in the additive of diet.