The present invention provides a process for removing an oxygenate impurity selected from aldehyde and/or ketone, from an olefinic product stream. A product stream is contacted with a metal oxide-containing catalyst in the presence of a C.sub.1 to C.sub.6 alcohol under conditions sufficient to convert the oxygenate impurity to an olefin and/or oxygenate of higher carbon number than the aldehyde and/or ketone. The aldehyde can be C.sub.2 to C.sub.5 aldehyde and the ketone can be C.sub.3 to C.sub.6 ketone. The metal oxide-containing catalyst typically comprises an oxide of at least one metal selected from the group consisting of Group 2 metals, Group 3 metals (including Lanthanide and Actinide series metals), and Group 4 metals.