From June to July 2000, specimens of Meretrix meretrix Linnaeus suffering from the / red muscle disease0(RMD) were co llected from Qinhuangdao District of Hebei Province, China. Abundant virus particles and their virogenic stroma were observed in the cytoplasm of the epithelium of digestive diverticula. The spherica-l shaped virions with the size of 50~ 80nm in diameter lack capsula. The inclusion bodies forming in the cytoplasm are multivesicular which assemble virus particles. In the infected cells w ith virus, the cellular organelles presented obvious pathological changes, e. g. the endoplasmic reticulum swelling and most ly turning into vesicles, the mitochondria dissolving or condensing, the nuclear membrane expanding, dissolving and forming nuclear vesicles, and the number of lysosome increasing.