(2E,4E,6R,10S)-4,6,10-Trimethyl-2,4-dodecadien-7-one 1 and its (6S,10S)-isomer were synthesized. The H-1 NMR spectrum of (6S,10S)-1 coincided with that reported for the major component of the sex pheromone of Matsucoccus feytaudi, which must therefore be either (6S,10S)- or (6R,10R)-1.