Abstract: The mongolian gerbil (Merious unguiculatus) was used as an experimental animal mo-del for studying the concurrent infections and pathogenicities with Entamoeba histolytica (E. h.) and Schistosoma japonicum (S. j.) by the cutaneous infection with 20 fresh cercariae of S. j, and the intracaecal inoculation of 5×105/0.5ml amebic suspension. Light and electron microscopy were used to observe the pathological changes of the caecal wall in the concurrent infections. The results showed that S. j. infection could promote the development of caecal amoebiasis, and stimulate symbiotic E. h. infection to develop invasive caecal amoebiasis. The pathological characteristics of the concurrent two infections not only exhibi- ted the characteristics of the single E. h. or S. j. infection, but also showed its own spe-cdality. Immunological effect of the host was apparently involved in the pathogenic process. In addition, the trophozoites of E. h. were usually observed to adhere closely to the egg shell of S. j. at the site of tissus necrosis. From the adherence phenomenon observed in our studies, there might exist an affinity mechanism between the E. h. trophozoite and S. j. ovum (Figs. 1-14).