Abstract: Background and Objective: Circumonchobothrium shindei is Ptychobothriid (Cestode) parasitizing the fresh water spiny eels of the family Mastacembelidae. The main objective of the study is to document the pathological changes induced by the pseudophyllidean cestode, Circumonchobothrium shindei in the intestine of Mastacembelus armatus (M. armatus). Materials and Methods: The Mastacembelid fishes were procured from the River Godavari during the year 2005-2009 and screened for the presence of ptychobothriid cestode and the normal and infected tissues of the fish were fixed, processed and permanent slides were prepared by the conventional techniques. Results: Histopathological changes include mechanical damage with desquamation of the epithelium, focal necrosis and increase in number of fibroblasts at the attachment point due to boring action of scolex. Vacuolation of sub-mucous cells and proliferative changes lead to the degeneration of the layers of the intestine. Muscularis layer does not show much damage. Parasites cause the dilation of blood vessels of the sub-mucosa resulting in degeneration of intestinal folds, shrinkage of villi and necrosis of epithelial cells. Villi get erupted at the region of attachment of the intestine. Inflammation and fibrosis associated with hyperplasia and metaplasia was observed. Increase in number of lymphocytes in the stratum granulosum and connective tissue layer was an indicative of inflammation. Conclusion: The main interpretation of the present study is that, the parasite is potentially pathogenic to the host and will certainly affect the fish productivity through mortalities, decreasing growth rate, declining the quality of the flesh and making the hosts more susceptible to secondary infections.