Taxan derivatives are produced efficiently and inexpensively, which are useful as oral-administrable antitumor compounds.A compound of formula (1) (wherein R1 is an alkyl group, an alkenyl group, an alkynyl group, a cycloalkyl group, an aryl group or a heterocyclic group; R2 is a hydroxyl group optionally having a protective group) is processed with an alkali metal permanganate to produce a compound of formula (2), which may be a starting material for oral-administrable antitumor compounds.