A new intestine microsporidium is suspected to be responsible for an severe emaciation disease of cultured grouper (including Epinephelus fuscoguttatus, E.drummondhayi, E.coioides and almost all grouper cultured in this waterway) fingerlings along Hainan coast of South China Sea.The disease generally occurred on juvenile fish with 7-10cm in body length and the prevalence and mortality varied in different farms, but the maximum can be up to 100％.The most remarkable clinical manifestation associated with this intestine microsporidiosis was stunted growth (see the following figure) and white feces.