Age effect on and diel periodicity in sex pheromone production, electroantennographic(EAG) assay for sex pheromone components and field bioassays were carried out to define the best blend of sex pheromone components in the Asian corn borer moth, Ostrinia furnacalis, in South Korea. Hexane extract of female abdominal tips contained three major compounds identified as tetradecanl acetate(14Ac), (E)-12-tetradecenyl acetate(E12-14Ac) and (Z)-12-tetradecenyl acetate(Z12-14Ac). E12-14Ac, Z12-14Ac and their 1 : 1 blend evoked strong EAG response on male antennae, but 14Ac did not. The amount of those three compounds in virgin females increased remarkably from the 2nd day after emergence to peak at the 3rd day and then decreased to the level of 1st day from the 4th day on. The mean ratios of 14Ac : E12-14Ac : Z12-14Ac were 0.91 : 1 : 1.38 and 0.74 : 1 : 1.36 in 2-day- and 3-day-old females, respectively, in the case of the individual washes and 0.7 : 1 : 1.51 in te case of the combined washes of 2-day- and 3-day-old females. Sex pheromone titers first detected at 2nd hour during the scotophase(16L/8D) and then gradually increased to reach the maximum level at the end of the scotophase. At corn-field trappings, the 1 : 2 blend was usually the most effective in attracting males among 12 blends(16 : 1, 5 : 1, 3 : 1, 2 : 1, 1.5 : 1, 1 : 1, 1 : 1.3, 1 : 1.5 : 1 ; 2, 1 : 3, 1 : 5 and 0 : 1) tested between E12-14Ac and Z12-14Ac, and the attractiveness of those blends generally increased as the content of Z12-14Ac increased to the level of the blend 1 : 2, then slowly decreased as the content of Z12-14Ac was more than twice over that of E12-14Ac. But the best blend in attracting males was 5 : 1 between E12-14Ac and Z12-14Ac at a ginger field, which should be further studied.