BACKGROUND: Cryptosporidium as an intracellular parasite causes severe diarrhea in calves. Several cases of cryptosporidiosis have been reported in different Iranian regions. OBJECTIVES: The aim of this study was to follow cryptosporidiosis occurrence in cattle husbandries of Semnan city in Iran. METHODS: Fecal samples were collected from 200 cows and calves, stained by modified Ziehl-Neelsen method and the cryptosporidium oocysts, size were determined. RESULTS: While the collected oocysts (n=40) showed a morphology similar to cryptosporidium parvum they were smaller than this parasite. In this respect, their mean length, width and length to width ratio were 3.44±0.06 µm, 3.55±0.06 µm and 1.03, respectively. By considering these characteristics and the small size of Cryptosporidium ryanae (as a key characteristic for this species) infection with this species has been suggested. However, further molecular studies would be necessary. The mean prevalence of cryptosporidiosis was 17.5%. However, in diarrheal calves, numbers of positive samples were significantly more than the other cattle. In non diarrheal cases, the infection rate was remarkably higher in cattle when compared with heifers and calves. There was not any relation between number of positive cases and type of husbandry, source of water, base of stable and sex of cattle. However, there was positive correlation between number of infected cattle and quality of basement sanitation, the way of using detergents and number of cattle in husbandry. CONCLUSIONS: It can be concluded that cryptosporidium ryanae may affect cattle of husbandries in some Iranian regions as Semnan. Hence, improvement of management and good sanitation of husbandry should be considered as control measures.