Abstract: The Haplosporidium spp. were characterized by oval spores possessing an operculum covering the orifice, which gave the spore a slightly flattened look on one end when observed under a light microscope. They were described as being a group of parasitic protists that form uni-nucleated spores without polar capsules or polar filaments. Presently, there are fifteen named Haplosporidium species found in freshwater oligochaetes and molluscs and in marine molluscs, crustacea, urochordates, echinoderms, and polychaetes. The present paper is the first report of its new member Haplosporidium babyloniae occurring on Babylonia areolata the southern coastal areas of China. Thereafter, the pathological and epidemiology features as well as the diagnostic methods were studied herein. The results showed that the organs of B. areolata, including the proboscis, foot muscle, intestine, digestive gland, stomach, liver and gill etc., were badly damaged and a series of serious lesions were caused. At the end, the therapy method was also put forward in order to control this disease.