The growth rate of fingerling grass carp fed on diet without manganese (Mn) was poor. Also, the rate of occurence of dwarf - fish was high, while the Mn content of vertebrae was low in the fish fed on diet without Mn content. The Mn content of vertebrae increased and reached a plateau in the fish fed on a diet containing supplementary Mn at a level of more than 15 mg kg-1 The percentage of liver weight, liver lipid content and the activity of plasma alkaline phosphatase (ALP) of the fish fed diet without Mn content were higher than those of the fish fed with Mn supplemented diets. Eight hematological characteristics (RBC, Hb, Ht, MCV, MCH, MCHC, PTP and PGC) were not affected by the Mn - containing diet- The optimal demand for Mn in a diet was about 15 mg kg-1 for fingerling grass carp.