Abstract:Two compounds, Z5—C(12)OAC and Z5—C(14)OAC were found in the washings of female ovipositors and sex pheromone glands of the Cossus mongolicus Ersch. through comparative analysis with capillary GC and GC MS. Among the two compounds only Z5—C(12)OAC caused strong EAG response of the male Cossus mongolicus Ersch. and showed obvious attraction in the trapping tests in two years and potential use for this pest control. The results testified that Z5—C(12)OAC was a major sex pheromone component of the Cossus mongolicus Ersch.