The invention relates to a process for preparing phytofluene of the formula I, ##STR00001## where a) a phosphonium salt of the formula II is condensed with an aldehyde of the formula III ##STR00002## in a Wittig reaction to give an acetal of the formula IV ##STR00003## b) the condensation product of the formula IV is subjected to an acid-catalyzed acetal hydrolysis to give the aldehyde of the formula V ##STR00004## c) and V is condensed in a further Wittig reaction with a phosphonium salt of the formula VI to give phytofluene ##STR00005## where the radicals R.sup.1, R.sup.2 and R.sup.7, and X.sup.- and Y.sup.- have the meaning sated in the description.