Abstract: Background :Cryptosporidiosis is a zoonotic disease and causes diarrhea syndrome in newborn lambs and calves. This disease is caused by an intracellular and extracellular parasite called Cryptosporidium. This parasite is transmitted via fecal-oral route. Complications of this disease in ruminants are: diarrhea, reduced growth, abdominal pain, lethargy. This protozoan has oocysts that are resistant to adverse environmental conditions and an effective drug that can be effective on the protozoan is not available. Materials and Methods :The aim of this study was to determine the infection with cryptosporidium in lambs in the suburbs of Quchan city. In this research, 202 fecal samples were collected from some villages of Quchan city from lambs aged 5 to 90 days during the winter season of 2022 to mid-summer of 2022. Fecal samples were mixed with the same volume of 2.5% potassium dichromate and transferred to the parasitology laboratory. At the same time, the risk factors include age, sex, breed, rectal temperature, fecal consistency, eating colostrum at birth, type of sheep farming, presence of other animals, type of corral, type of bedding, type of water trough and herd size were gathered in special registration questionnaires. Fecal smear was prepared and stained by Zeihl-Nelson method. The samples were observed with 40X and 100X light microscope. In the current research, the intensity of pollution in the expansions was determined based on the method of Ahamed et al. (2015). Results: Out of 202 fecal samples, 20 positive samples (9.9%) were reported. The lowest intensity of infection (1+) was in 11 samples (55%) and the average intensity of infection (2+) was in 9 samples (45%). In this study, high intensity contamination (3+) was not found. Conclusion: In the present study, no significant relationship was found between the frequency of cryptosporidium infection and risk factors such as age, gender, race, body temperature, fecal consistency, type of sheep farming, herd size, type of corral, type of bedding and type of water consumed

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