The present invention relates to a process for selectively producing C.sub.3 olefins from a catalytically cracked or thermally cracked naphtha stream by fractionating the naphtha feed to obtain a C.sub.6 fraction and feeding the C.sub.6 fraction either in the riser downstream of the injection point for the reminder of the naphtha feed, in the stripper, and/or in the dilute phase immediately downstream or above the stripper of a process unit.