Mushroom production units of Kermanshah province were sampled during 2012-13, and 50 fungal isolates were obtained. Verticillium fungicola with the most number of isolates, Tricoderma harzianum and Trichothecium sp. were the most frequent fungi associated with the cultivated mushroom, Agaricus bisporus. Seven isolates were obtained from the cap of A. bisporus with following characteristics: colony white to gray (Fig. 1a and b), vegetative hyphae colorless, aseptate, branched and 4/5–14 µm diam (Fig. 1c). Sporangiophores solitary, erect, unbranched, variable in size, 130–200 µm long, anchored at base by four to five rhizoids, 15–20 µm long, diam 2–3 µm and with an apex that coils or less commonly remains straight and becomes moniliform (Fig. 1e and f). Sporangia globose, white to brownish, 43 (36–57) µm in diam (Fig. 1g-i). Sporangiospores ellipsoid, continuous, 5 (3–7) × 9/5 (6–12) µm (Fig. 1j). The isolates were identified as Helicocephalum sarcophilum Thaxter (Helicocephalidaceae, Zoopagomycotina), based on the morphological characters. According to the published data, this the first report of the species for mycobiota. Moreover, this is the first report of Helicocephalum associated with A. bisporus for the world (Borowska1997; Drechsler 1934; Kitz and Embree 1989; Roux 1996). Species of Helicocephalum are not reported in the literature often and new taxa are rarely described. The isolates are kept in the fungal collection of the Department of Plant Protection, Razi University, Kermanshah, Iran.