To determine the requirement dose of lysine during stages of growth of Ctenopharyngodon idellus,the growth rates of fingerling grass carp which fed in different levels of lysine were tested.In addition,the free lysine levels of serum,liver and muscle of fingerling grass carp were detected.The results showed that the requirement dose of lysine in feedstuff was 1.61% which was determined by the results of the maximum of growth rates,and the requirement dose of lysine in feedstuff were 1.28%,1.46% and 1.49% which were determined by the results of free lysine levels of serum,liver and muscle respectively.The requirement dose of lysine in feedstuff which was determined by the results of free lysine levels of serum was lower than that the results of growth rates,while the requirement doses of lysine in feedstuff which were determined by the results of free lysine levels of liver and muscle were close to the results of growth rates.