International Journal of Preventive Medicine (Int J Prev Med)2008-78021292021102025262526ENDepartment of Parasitology and Mycology, School of Medicine and Infectious Diseases and Tropical Medicine Research Center, Isfahan University of Medical Sciences, IsfahanDepartment of Parasitology and Mycology, School of Medicine and Infectious Diseases and Tropical Medicine Research Center, Isfahan University of Medical Sciences, IsfahanIntegrative Functional Gastroenterology Research Centre, Isfahan University of Medical Sciences & Department of Internal Medicine, School of Medicine, Isfahan University of Medical Sciences, IsfahanDepartment of Medical Parasitology and Mycology, School of Public Health, TehranDepartment of Biostatistics and Epidemiology, School of Health, Isfahan University of Medical Sciences, IsfahanDepartment of Parasitology and Mycology, School of Medicine and Infectious Diseases and Tropical Medicine Research Center, Isfahan University of Medical Sciences, Isfahan20211019Background: Determination of the prevalence of intestinal protozoan infection is a fundamental step to set up an effective control program to improve the health status of society and to establish efficient strategies. Intestinal pathogen and even non‑pathogen protozoa consider as major causes of disease in patients with gastrointestinal problems. The objective of this study is to determine the prevalence of intestinal protozoan infection in patients with ulcerative colitis (UC) in Isfahan, Iran. Methods: The descriptive cross‑sectional study carried out from 2013 to 2018 in Isfahan, Iran. One thousand nine hundred and sixty‑five samples of feces from patients with UC collected and each sample examined using direct wet mounting with normal saline and iodine and sedimentation tests such as formol‑ethyl acetate concentration and trichrome‑staining methods. Results: From 655 patients, 185 (28.2%) infected with Giardia lamblia followed by Blastocystis hominis (27.3%), Endolimax nana (14.4%), Entamoeba coli (11.5%), Iodamoba butschlii  (4.7%), Entamoeba histolytica (1.4%), and Chilomastix mesnili (0.6%). Conclusions: This study revealed a high prevalence of infection with at least one or six non‑pathogenic and pathogenic intestinal protozoa in UC patients in the Isfahan region. Intestinal protozoa are a challenging public health problem wherever health care is limited in the area. The emergence of UC in the world results in the need to study etiologic factors. In order to obtain further information about the etiology of disease, we investigated the prevalence of intestinal protozoan infection in patients with UC in Isfahan, Iran.http://ijpm.mui.ac.ir/index.php/ijpm/article/view/2526http://ijpm.mui.ac.ir/index.php/ijpm/article/download/2526/717718380