Described is a process for hydroformylation of an olefinic compound, which comprises, carrying out the reaction in the presence of: a) a rhodium compound, b) a tertiary organic phosphorus compound represented by the following formula (1): P(X.sub.1)(X.sub.2)(X.sub.3 --SO.sub.3 M) (1) wherein X.sub.1 and X.sub.2 each independently represents a monovalent hydrocarbon group having 1-15 carbon atoms and X.sub.3 represents a divalent hydrocarbon group having 1-15 carbon atoms and M represents an alkali metal, and c) a polar organic compound; separating the rhodium compound, the tertiary organic phosphorus compound represented by the formula (1) and the polar organic compound from the resulting reaction mixture by extraction with water; subjecting the extracted water layer to removal of water and addition of at least one acidic substance selected from sulfonic acids to prepare a concentrate containing the rhodium compound, the tertiary organic phosphorus compound represented by the formula (1) and the polar organic compound; and recycling the resulting concentrate to a reactor for reuse.