In this research,for taxonomic studies and identification of the fungi associated with the powdery mildew(Oidium euonymi- japonici) of Buxus trees (Euonymus japonica), the infected leaves were collected during autumn and winter 2012-2013 in Gorgan (Golestan province -Iran). The samples after washing and surface sterilizing, were cultured on PDA medium(with boxwood extract).Then based on available credible resources, fungi Epicoccum nigrum (Synonym: Epicoccum purpurascens) ، Ampelomyces quisqualis Ces. ex Schlech  and Phoma sect hetrospora were isolated and identified. E.nigrum produced cottony or felty colonies that were yellow to orange initially and became greenish brown by aging. Black dots with diameter 100-200µm were observed macroscopically on the colony surface and were called sporodochia. The hyphae were observed septate and yellow to brown in color after 3 days. Conidiophores form clusters and young conidia were round, non septate and pale in color. Mature conidia with diameter 15-25 µm were observed brown to black in color with rough surface, contain multiple transverse and vertical septa and had a funnel shaped base. A. quisqualis formed globose, pyriform pycnidia with different dimensions behind the leaf. Pycnidium was golden yellow when young, and yellowish to brown at maturity, unilocular with a thick wall, no distinct ostiolum; dehiscence by apical rupture of pycnidium. Conidiophores were absent and conidia were  found hyaline, ellipsoidal with dimensions 3-4 µm. Based on scientific resources, this fungus has been found as a mycoparasite of powdery mildew. Phoma sect phoma produced dark olivaceous colony and pycnidia had been found as single or multiple, sub globose with diameter 110-180 µm. Pycniospores were abundant, mainely oval or spherical with diameter 1.5-2.5 µm. Based on this information, above fungi are reported as new records for Iran mycroflora.