The present invention relates to a process for producing 4-alkoxycarbonyl-2-oxazolidinone compound represented by the formula (III): wherein R1 represents H, an alkyl group, an cycloalkyl group, an alkenyl group or a phenyl group, R2 represents H, an alkyl group, a phenyl group or an alkenyl group, R3 represents an alkyl group, a cycloalkyl group, an alkenyl group, or a phenyl group, and R4 represents H, an alkyl group, an alkenyl group, acycloalkyl group, alkynyl group, an aryl group, a 5- or 6-membered heteroaromatic ring group, an alkoxycarbonyl group, an acetyl group or a benzoyl group, which comprises reacting a 5-alkoxy-2(3H)oxazolone compound represented by the formula (I): wherein R1, R2 and R3 have the same meanings as defined above, and an aldehyde compound represented by the formula (II): R4CHO  (II) wherein R4 has the same meaning as defined above, in the presence of a Lewis acid catalyst.