PURPOSE: To obtain the titled substance containing no water with little energy, by bringing an aqueous solution containing 4-hydroxybutyraldehyde into contact with an alcohol, separating two liquid phases, and catalytically hydrogenating the organic phase to give a nonacidic reaction solution containing a little amount of water.

CONSTITUTION: An aqueous solution containing 4-hydoxybutyraldehyde obtained by the hydoformylation of allyl alcohol, etc. is brought into contact with an alcohol, and the phase separation is carried out to give an organic phase, which is then catalytically hydogenated to afford the titled substance. An alcohol, having as low a solubility in water as possbile, and capable of capturing the 4-hydroxybutyraldehyde efficiently in the organic phase is selected from liquid alcohols capable of separating from water. A 4W8C monohydric alcohol is particularly preferred. The alcohol regenerative on catalytic hydrogenation is permitted if it reacts with the aldehyde.

EFFECT: Reduced corrosion of reactors or bad influence on the catalyst.