The pathogen of wilt disease of poinsettia was identified as Fusarium oxysporum schl. f. sp. euphorbiae Z. D. Jiang et P. K. Chi. f. sp. nov. according to its morphology, cultural character and pathogenicity. This pathogen only attacked poisettia among 14 species of plants on 11 families by the methods of impregnated inoculation and irrigated inoculation. The disease could cause basal stem rotted in the late stage.