Continuous process for performing a polyphasic aldol condensation reaction to give mixed α, β-unsaturated aldehydes in a tubular reactor by reaction of two different aliphatic aldehydes selected from acetaldehyde, propionaldehyde, n-butyraldehyde, isobutyraldehyde, n-pentanal, 2-methylbutanal or 3-methylbutanal, characterized in that the aliphatic aldehydes are mixed separately in a molar ratio of 1:1 to 3:1, then the aldehyde mixture and an aqueous solution of a basic compound are introduced via the base into an upright tubular reactor in cocurrent mode, the aqueous solution of the basic compound forming the continuous phase which flows through the tubular reactor under laminar conditions, and the aldehyde mixture forming the phase dispersed in droplet form in the continuous phase and the aldol condensation reaction being performed at a temperature up to 90° C. and the tubular reactor being operated with a space velocity V/Vh of the aldehyde mixture per unit reactor volume and time of 0.1 to 1.3.