Abstract: In a process for producing an alcohol by hydroformylation comprises reacting a straight chained, branched or alicyclic mono-olefin having from 3 to 20 carbon atoms with carbon monoxide and hydrogen to form an alcohol having carbon atoms greater in number by one than the carbon atoms of the mono-olefin, the improvement comprises(a) a fist step in which the mono-olefin is hydroformylated with use of a cobalt catalyst in the presence of a gas mixture of carbon monoxide and hydrogen at a high temperature under high pressure to selectively form an aldehyde at a conversion of the mono-olefin being from 50 to 95 mol % while suppressing the formation of an alcohol, and the cobalt catalyst is then removed from the unreacted olefin and the formed aldehyde by decomposition or extraction, and(b) a second step in which the mixture of the unreacted mono-olefin and the formed aldehyde freed from the cobalt catalyst in the first step is reacted with a gas mixture of carbon monoxide and hydrogen with use of a cobalt organopho