the present work was aimed to investigate the endemicity of Cryptosporidium parvum (The coccidian intestinal protozoan of man and other grazing animals)in some districts of Nineveh province, then evaluating the histopathological effects of the isolated parasite in inoculated mice. A total of 200 child those attended healthcare centers and diagnosed clinically to have persistent and chronic diarrhea were chose for the study. There ages were ranged from ≤1 to ≥5 years old. Their families were practicing livestock grazing. The study were performed between October 2020 and March 2021, in 5 districts : Al- Hamdania, Bartelah, Basheqah, Fadhliah and Kokgali; respectively. Blood and stool sample were taken from each patient. Depending on direct and immunodiagnostic methods, the highest infection percentage was recorded in Kokgali district (48.1%), and the lowest was recorded in Bartelah district (27.2%). The percentage of positive cases were varied according to the performed diagnostic method: ELISA technique for stool samples (40%), ELISA technique for blood samples (36%), Zeil Neelsen stain (35% ) and flotation method (30%). Infection percentage in males (44.7%)was higher than females (35.7%). Considering age groups, 3-5 years group was more likely to get cryptosporediasis infection(56% of the positive cases). Inoculation of the parasite in lab mice showed obvious histopathological changes, especially in the epithelial brush bordered cells of intestine.