Abstract: A process including a first stage wherein a feed gas stream containing acrolein originating, for example from the gas-phase oxidation of propylene to acrolein, is fractionated into a gaseous effluent and a liquid stream in a cooling column operating such that the temperature of the liquid stream at the bottom of the column is lower than or equal to the condensation temperature of the feed gas stream, the difference in temperature not exceeding 20.degree. C. and, a second stage, wherein the gaseous effluent is condensed at a temperature that is lower than 20.degree. C., to give a liquid fraction and a purified gaseous fraction, is disclosed. An apparatus for carrying on the purification process is also disclosed.