We had cloned and characterized a gene from Fusarium oxysporum designated FCD1, encoding a putative cellobiose: quinone oxidoreductase (CBQ) which is a member of the extracellular redox enzyme family and also a member of glucose-methanol-choline (GMC) oxidoreductases. CBQ is known to be a free flavin domain of a cellobiose dehydrogenase (CDH) generated by proteolysis, but FCD1 gene encodes CBQ directly. In a phylogenetic tree of amino acid sequences of FCD1, GMC oxidoreductases and hypothetical GMC oxidoreductases, FCD1 clustered together with flavin domains (CBQs) of CDHs and putative proteins with unknown function of ascomycetes. FCD1-disruptants showed no reduction in virulence toward tomato and no obvious morphological effects such as production of conidia and mycelial growth as compared to the wild type strain, suggesting that FCD1 is not essential for virulence and vigor in F. oxysporum.