A method for the hydroformylation of an olefinic compound through a reaction of the olefinic compound with hydrogen and carbon monoxide, which comprises effecting the reaction in the presence of: (a) a rhodium compound; (b) a tertiary organophosphorus compound represented by the following general formula (1): P(X1)(X2)(X3-SO3M), wherein X1 and X2 represent each a monovalent C1-15 hydrocarbon group; X3 represents a divalent C1-15 hydrocarbon group; and M represents an alkali metal; and (c) an organic polar compound; extracting the obtained reaction mixture with water to thereby separate the rhodium compound, the compound of the formula (1) and the organic polar compound therefrom; eliminating water from the aqueous layer thus separated; adding thereto at least one acidic material selected from the group consisting of sulfonic acids to thereby give a concentrate containing the compound of the formula (1) and the organic polar compound; and circulating this concentrate into the reactor for reusing the same.
