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Abstract Background and Objective: In many countries, especially in developing countries, diarrheal diseases is one of the most important causes of mortality. In these countries, due to availability transfer conditions of parasitic infections, (pathogenic and non-pathogenic parasite), have a high prevalence. This study aimed was determining the prevalence of Parasites causing diarrhea in Gorgan . Material and Methods: This cross-sectional study was performed on 1086 Patients with acute diarrhea. The test was performing by the wetmount and formalin-ether concentration method according to WHO protocol. Results: From 1086 patients in study, 197 (18.1%) were infected by intestinal parasites, that 141 (13%) were infected with Protozoan and 79 (7.27%) were infected with intestinal worms. The prevalence of wet mount method was, Entamoebahistolytica in 69 (6.4%), Giardia lamblia in 27 (2.5%), Entamoeba coli in 15 (1.4%), Chilomastixmesnili in 8 (0.7%), and with formalin-ether method was Hymenolepis nana in 26 (2.4%), Trichostrongylus in 16 (1.5%), Enterobiusvermicularis in 10 (0.9%). Conclusion: The high prevalence of Entamoeba histolytica, is indicating protozoan importance as a cause of acute diarrhea. Keywords: Intestinal Parasites Diarrhea Wetmount Formalin Ether Gorgan