Background: Toxocara vitulorum is a involved in the Ascaridoidea family and is a large roundworm with a semi translucent, soft body surface and pinkish color. Female worms measure 8-30cm in length, male worms 6-25cm. The major hosts of T. vitulorum are buffalo (Bubalus bubalis) and cattle (Bos species) in the humid tropics of Asia, Africa and South America. The diagnosis of T. vitulorum infections is usually made by observing characteristic eggs in routine fecal examination. Serological methods are also used to diagnose Toxocariasis. However, in recent years, PCR, a new generation molecular diagnostic method, has been used. The genetic structure of T. vitulorum is little known compared with data available from other parasites. The present sutudy was designed to determine the T. vitulorum isolates by the genetic characterization of the mitochondrial cytochrome c oxidase subunit I (cox1) gene.