Pathogens cultivation and histopathological observation was made on Fugu obscurus with the symptom of ulceration. Microscope examination on ulcers and muscle tissues which infected with fungal mycelium that was coarse, without branch, Gram staining positive. Heart, liver, spleen and intestine contained small amount of inflammatory cell invasion without fungal mycelium and obvious pathological changes. The result of Sabouraud medium culture with the temperature of 37℃ as follow: Mycelia had pale yellow spherical sporangium after 24 h; mycelium appeared, the sporangium matured and oval spores released after 72 h; glass utensil was full of colony after 120 h. Pathological examination of subcutaneous ulcer and muscle revealed that a large number mycelia and inflammatory cell invaded subcutaneous tissue, which caused neighboring muscle tissue degeneration, necrosis and interstitial edema; Coarse hyphae penetrated mucosal into the basement with the result of small vascular embolization at the same time. Mycelium contained blue color and branch looked like a right angle. According to Ainsworth classification system, the pathogen was identified as Mucor sp.