Abstract: From dogs Infected successivcly with a total number of 900 cercariae of S. japonicum two ycars ago, sections of colonic mucosa with obvious granulomatous lesions were studied under electron microscope and compared with those of the healthy dogs. The results showed that the epithelial cells of the colonic mucosa selected from different sites with hypertrophict granulomatous and ulcerative lesions, had the characteristics of both proliferative and adcnomatous ccllular changes (Figs. 2-5). But, as comparel with the ultrastructure of the colonic cpithelium of the normal, the characteristics of the schistosomal lesions was more of the proliferative type rather than of carcinomatousone,