Two new species of Pythium Pringsheim isolated from soils of northwestern regions in Iran, are described: P. monoclinum Abrinbana, Abdollahz. & Badali, sp. nov., and P. iranense, sp. nov. Both species are morphologically distinct from all known species. Pythium monoclinum Abrinbana, Abdollahz. & Badali, sp. nov., is morphologically characterized by the presence of a swollen element in oogonial stalks below terminal oogonia, mostly monoclinous antheridia originating at various distances from the oogonia that occasionally arising from inflated part of oogonial stalk and, rarely production of peanut-shaped and double oospores. Pythium iranense, sp. nov., is distinguished from other species of the genus by the production of smooth-walled oogonia that occasionally have 1-3 papillae, globose to rarely elongated oogonia, 1-2(-5) antheridia per oogonium or crowd of antheridia around oogonia, 1-2 rarely 3-4 oospores per oogonium, rarely peanut-shaped oospores and immature oospores provided with 1-6 projections. Phylogenetic relationships of the isolates belonging to these new species with other related species were investigated using internal transcribed spacers of rRNA genes and partial cytochrome c oxidase subunit I sequence data. The phylogenetic analyses separated the two species from closely related species and placed P. iranense, sp. nov., in clade J1 but the clade of P. monoclinum Abrinbana, Abdollahz. & Badali, sp. nov., was unknown.