Ascotis selenaria, one of the major Geometridae moths, annually damages the citrus leaves and fruits. This study was focused to identify the sex pheromone components of A. selenaria in order to monitoring and control its population. Adult female and male were usually emerged at the time between 2 hour before and 2 hour afterlights-off in 16L:8D photoperiod. Mating, irrespective in female age, started at 2 hour after lights-off and peaked between 4 hour and 6 hour after lights-off. They copulated for 3 hour 47 min per pair. Gland extract of virgin female was analyzed with GC-MS and GC-EAD.Z,Z-6,9-3,4 epoxy nonadecadiene (Z,Z-6,9-3,4 epo- 19Hy) was identified as the candidate. Both of stereo isomer, Z,Z-6,9-3R,4S epo- 19Hy and Z,Z-6,9-3S,4R epo- 19Hy, showed a strong EAG response in male antennae. Further study like field attraction test should be needed to clarify the sex pheromone composition and in A. selenaria. Age and time were related with the amount of sex pheromone components biosynthesized in A. selenaria gland. 0 day old female had 112.7ng per gland at 5 hour after lights off and the amount was decreased as they aged. The sex pheromone biosynthesis started from lights-off and showed the increasing tendency during scotophase.