A 2-('omega'-alkoxycarbonylalkanoyl)-4-butanolide is produced in a high yield with a good selectivity by the condensation reaction of 'gamma'-butyrolactone with a readily available, inexpensive dicarboxylic ester represented by the following general formula: ROOC(CH2)n Coor (wherein n is 7 to 13; and R represents alkyl or alkenyl). A long-chain 'omega'-hydroxy carboxylic acid is produced by hydrolyzing and decarboxylating the above butanolide and reducing the carbonyl group of the obtained product into a methylene group.