The mating behavior of the diamondback moth (DBM), Plutella xylastella, was actively observed from 2 h post-scotophase and maintained up to 2 h post-photophase. The pheromone glands of DBM populations in Korea were extracted with hexane and gas chromatograph (GC) analysis showed that three major components of sex pheromone, (Z)-11-hexadecenal (Z11-16:Al), (Z)-11-hexadecenyl acetate (Z11-16:Ac) and (Z)-11-hexadecenyl alcohol (Z11-16:OH), were identified at the ratio of 8:3:2. To contrast, Z11-16:OH was not detected from Solid Phase Microextraction for the sex pheromone emitted during the scotophase. Both Z11-16:Al and Z11-16:Ac elicited the antennal response of male DBM in GC-electroantennographic detection and electroantennogram (EAG) assay. EAG assay revealed that the ratio of major components, Z11-16:Al and Z11-16:Ac, in the blend of 5:5 and 7:3 strongly attracted DBM male adults. The minor components, 0.5% of Z11-16:OH or 5 to 10% of (Z)-9-tetradecenyl acetate (Z9-14:Ac) also elicited the EAG response when mixed with major components blends at the ratio of 10:10 between Z11-16:Ac and Z11-16:Al, suggesting these components affect the activity of major components of sex pheromone.