Abstract: Echinococcus granulosus is widely distributed throughout Iraq. Characteristics of E. granulosus strobila are presented from dogs experimentally infected with protoscoleces from hydatid cyst isolated from the lungs of a domestic sheep in Nineveh Province. They were defined and compared with those of other recognized strains of this parasite. The number, shape and arrangement of rostellar hooks of adult worms and detailed description of male and female genitalea were taken into consideration as key criteria. Adult cestodes are characterized mainly by 32.2-34.8 hooks highly variable in shape and size, 42.8-34.2 testes situated either throughout the proglottis with one rows behind the vitellin gland or they do not exceed the anterior half of the vitelline gland, the ovary variable in shape from compact lung-shaped to elongated with well-demarcated lobules forms. The results revealed the existence of two distinct strains similar to dog/sheep and dog/cattle strains.