1. The microsporidiosis was found on Priacantus tayenus from the Beibu Wan inNan Hai of China. The gonads were heavily infected by the parasites which renderthe majority of the fish lost their reproductivity. 2. The pathogenic agent of this disease is found to be a new species of the genusPlistophora and is here named Plistophora priacanthicola. The spores are ellipsoidalto shape the anterior end is narrower than the posterior end. The size of the spores: length 5.45 (4.9-60)μ, width 3.14 (3.1-3.3)μ; lenthof the polar filament 80-429μ. It resembles somewhat to P. longifillis, P. ovariae, P.oolytica and P. mirandellae, but differs from them in large size of cysts. 3. The infective rate of the parasites increases with the age of the host andthere is no variation with the sex and seasonal changes.