During August 2003, symptoms of canker were observed in Platanus×acerifolia trees planted along the streets of Tokyo and Saitama, Japan. These trees exhibited signs of the disease around the cut ends of pruned branches toward the trunk, with the lesions turning purplish to dark brown and surrounded by a yellowish discoloration. In cases where a lesion reached the trunk, the spread was downward, resembling the trickling of water. Thereafter, the bark became brown to pale brown with a shark skin-like texture. Some lesions withered and exfoliated, leading to the death of the afflicted branches. In samples of the exfoliated bark, some filamentous fungi forming ascocarps and conidiomata were detected. From these samples, we established isolates through single spore isolation. Each of the isolates was cultured and then inoculated into the bark of a Platanus×acerifolia tree with or without scarring the inoculated area. As a result, only the scarred area into which an ascospore-derived isolate was inoculated reproduced the initial symptoms. With the inoculated strain re-isolated from the lesion, its pathogenicity was confirmed. This ascocarp-forming pathogenic fungus was identified as Neofusicoccum parvum according to the base sequences of the rDNA ITS region and TEF1-α gene.