The aerial concentration of a synthetic sex pheromone component (Z-11-tetradecenyl acetate) and the mating ratio of tethered females of the smaller tea tortrix were measured under field conditions. The aerial concentration of the pheromone component and mating ratio show a logarithmic linear relationship. The aerial concentration of the synthetic pheromone component should be more than 20 ng/m3 to suppress the mating to less than 30%.