The present invention relates to an improved process for preparing 2,7-dimethylocta-2,4,6-trienedial of the formula I, ##STR00001## by a) double enol ether condensation of a butenedial bisacetal of the formula II with an enol ether of the formula III, ##STR00002## in the presence of a Lewis acid catalyst to give a condensation product of the formula IV, ##STR00003## where the radicals R.sub.1 and R.sub.2 in formulae II to IV are independently of one another C.sub.1-C.sub.6-alkyl;b) hydrolysis of the acetal groups of IV by adding an aqueous acid to form the dialdehyde of the formula V; ##STR00004## d) crystallization of I from the reaction mixture,Wherein process steps a) to d) are carried out in the presence of an inert, water-immiscible organic solvent.
