Parasitic gastrointestinal infections are one of the most important health problems in the developing countries, which lead to the onset of intestinal disease particularly diarrhoea. Due to the particular geographic situation in the Mazandaran province, individuals are infected with various intestinal parasites. The aim of this study was to determine the prevalence rate of enteropathogenic parasites in the patients with gastroenteritis living at the east of Mazandaran province (Sari, Nekah and Joybar cities), northern Iran. This descriptive study was carried out from September 2009 to March 2010. Faecal samples were collected by randomized cluster method from 962 patients with gastroenteritis who were refered to the Health Service Centers of Sari, Neka and Joybar cities. All data about the patients were recorded in questionnaire. Stool specimens were examined by direct wet mounting, formolether concentration, and Ziehl-Neelsen acid fast stain and Auramin Phenol fluorescence (APF) method for the investigation of Cryptosporidium and Isospora. Prevalence of intestinal parasites and their relationship with gender, age, and season were investigated, and the obtained data were analyzed with χ² test using the SPSS software (16.0). Out of 962 patients with gastroenteritis, overall infection was 9.1%; Giardia lamblia (4.1%) with the highest and Enterobius vermicularis (0.2%) with the lowest prevalence rate. Prevalence rate of other parasites were as follow: Cryptosporidium, 0.1%; Entamoeba histolytica, 0.1%; Chilomastix mesnili, 0.1%; Entamoeba coli, 1.2%; Blastocytis hominis, 1.8%; Trichostrongylus spp., 0.4% and Hymenolepis nana, 0.9%. Findings showed that Giardia is the most common cause of intestinal infection at the east of Mazandaran province, and could be defined as the most important parasitic agent of gastroenteritis. On the other hand, infection with enteropathogenic parasites as compared with the previous reports showed significant decline, which reveals the coverage of health education, increase of public knowledge on the parasitic diseases and sanitation of living environment.