BACKGROUNDS: All helminthes belonging to the phylum Acantocephala are obligatory parasites which are reported to be found in the gastrointestinal tract of definitive hosts such as fish worldwide and in Iran as well. OBJECTIVES: The purpose of this study was undertaken to determine the frequency and pathological changes in the gastrointestinal tract of the Barbus sp. due to Neoechinorhynchus sp. METHODS: over a one year period, 89 fish (Barbus sp.) were collected from the Zarine-Roud River. Intestines were removed and investigated for infection. Histopathological sections were prepared and stained in a routine manner using the hematoxylin-eosin method. RESULTS: The prevalence of gastrointestinal infection with Neoechinorhynchus sp. in Barbus sp. was 16%. Histopathological lesions were revealed epithelial thickness and folding. As a result of mechanical irritation, the Fibrinous enteritis with epithelial hyperplasia was developed. In the lamina properia and mucosa of the intestine, the vessels dilated and congested. Mucosa folding sections, hyperemia and inflammatory cell infiltration including eosinophile, lymphocyte and fibrinous were noted. CONCLUSIONS: It was concluded that Barbus fish infected by the Neoechinorhynchus species from the Zarine-Roud River, are not suitable for pond fish cultivation in the region and this can be cause for of severe economic losses.