Oncomelania hupensis, an intermediate host of Schistosoma japonicum, remains an important public health problem. Haemocytes play an important role in an innate immunity defense system of O. hupensis and require more research. The present study provides information concerning the morphological and functional basis of defense cells of O. hupensis observed through optical microscopy and electron microscopy [scanning electron microscopy (SEM) and transmission electron microscopy (TEM)]. In this study, two types of haemocyte cell categories, type I (macrophage-like) and type II (lymphocyte-like), were distinguished according to shape, size, surface structure, internal structure, functions, structure of cytoplasm and the processes of spike-like filopodia. The results showed that type II cells generally were smaller than type I cells. In addition, only type I cells had the ability to adhere to sheep red blood cells (SRBC) after 60 minutes of incubation. The adherence to SRBC of type I cells represents adhesion activity of these cells to foreign particles or parasites. These results warrant further investigation to better understand the function of O. hupensis haemocytes. The present study confirms several previous findings concerning haemocytes of O. hupensis and opens the door for further research into the function and structure of O. hupensis haemocytes.