A method is described for processing an olefin-containing product stream (1) that contains, besides ethylene and propylene, longer-chain olefins and compounds of hydrocarbons with oxygen (oxygenates). Such a product stream (I) can occur in particular in olefin synthesis from methanol. The product stream is dewatered in successive process steps, optionally compressed in several steps and dried. Then it is subjected to fractionation. For removal of the undesired oxygenates it is proposed that the oxygenates be washed out of the gaseous product stream after the compression steps and before the drying step in a column (12) with methanol.