A novel fructosylamine oxidase derived from yeast Pichia sp. and a gene coding for the enzyme are disclosed. The fructosylamine oxidase may be produced by culturing the transformant which has been transformed with a recombinant vector comprising the DNA fragment containing the fructosylamine oxidase gene. Since the fructosylamine oxidase oxidizes fructosyl valine, it may be used in an assay for fructosyl valine. The assay kit and enzyme sensor comprising the fructosylamine oxidase of the invention are useful in measurement of glycated hemoglobin.