The systematics of the Ostertagiinae is unsettled with no agreement on how many genera and species are present in cattle and sheep. Ten species of Ostertagiinae are commonly parasitic in cattle and sheep. In the global fauna, six of 13 ostertagiine genera are endemic to Iran. The life cycle of Ostertaginae is direct and ingested thirdstage larvae after exsheatment in the rumen, penetrate the gastric glands in the abomasal mucosa where two parasitic moults occur before the L5 emerges from the gland. In the present work, Marshallagia marshalli and Ostertagia occidentalis, collected from the abomasums of sheep from Mashhad, Iran, is described. The association of light and scanning electron microscopy (SEM) allowed a detailed analysis of the morphology and ultrastructure of these nematodes. The male body length of M. marshalli and O. occidentalis were 9.3–10.20 and 9.60–10.50 mm, respectively. The female body length of M. marshalli and O. occidentalis were 10.10–15.30 and 10.4– 15.70 mm, respectively. One of cervical papillae is seen 333 and 250 μm from the anterior end of male and female body surface in O. occidentalis and 287.5 and 200 μm from the anterior end of male and female body surface in M. marshalli, respectively. The size of cervical papillae is 13.3 μm in male and 10 μm in female in O. occidentalis and 9.33 μm in male and 8.57 μm in female in M. marshalli. Some other taxonomic features of M. marshalli and O. occidentalis, such as details of cephalic region, the system of longitudinal and surface cuticular ridges (synlophe), the orientation of rays of the copulatory bursa, localization of vulva, morphology of vulvar flap, and posterior end of females are also documented by SEM.

Keywords