Root and crown rot is one of the most important fungal plant diseases which is observed in fields annually. One of these agents are Fusarium species which cause lots of damages to crops such as maize. In a survey in cereal fields in Lorestan and Ilam provinces in 2016, plants with fusarium root and crown rot symptoms were collected and were transferred to laboratory. In vitro experiments were started quickly. After isolation in Nash & Snyder and DCPA, isolates were purified and then were transferred to PDA, CLA, KCl, SNA and strile distilled water to microscopic observations. Macrocinidia, microconidia, conidiogenous cells, chlamydospores and colony features were studied according to diagnistic keys (Marasas, 1986; Leslie and Summerell, 2006). Results showed that isolated species were F. polyphialidicum Marasas. Average growth rate, white to pale orange aerial mycelium, white to yellow color in reverse colony on PDA were observed. Robust and large macroconidia with moderately curvature were produced in white sporodochium. Size of these spores were 4.5-6 × 35-65 µm, they were 5-7 septate, with foot shaped basal cell and tapering apical cell. Microconidia were clavate and 0-septate, and 2.5-3.5 × 35-65 µm. Monophialids and polyphialides and single, in pairs, clumps and in chains chlamydospores were another features of this species. According to above properties and identification, pathogenicity test were examined in greenhouse conditions according to Burgess et al. (1994) method. This is the first report of F. polyphialidicum on maize in Iran.