Abstract: From June to July 2000, specimens of Meretrix meretrix Linnaeus which suffered from the 0red muscle disease0( RMD) were collected from Qinhuangdao district of Hebei province.The rickettsia-like organisms (RLO) were found and observed in the digestive diverticula. There are two types of RLO inclusion bodies, one is basophilia and another is acidophilia, both of which observed are circularity or olivary shapes. By the electron microscope, the epithelial cells were filled with RLO, of which the shapes and sizes are different. The infected cells w ith RLO presented a series obvious pathological changes. The endoplasmic ret iculum swollen and mostly turned into vesicles, the ribosomes degenerated. The mitochondria dissolved or condensed. The nucleus underwent a series of changes including the chromatin condensing, nuclear membrane swelling and forming nuclear vesicles. At last, the nucleus and most of cellular organelles disappeared. The RLO in binary f ission and budding in the cytoplasm were observed.