Abstract: This paper deals with the biology, morphology and ecology of a barconid wasps, Ontsira palliatus (Cameron), ectoparasitic on the larvae of Semanotus sinoauster (Gressitt). Other aspects concerning this wasps are also discussed including its distribution in China, methods of reproduction, range of hosts and controlling pests in large area, etc. It is for the first time discovery that Semanotus sinoousteris parasitized by Ontsira palliatus. In China fir (Cunninghamia lanceolata) wood, the percentage of parasitization of Semanotus sinoauster at the contemporary generation is about 70—80% after artificial release, and that of actual control effect is about 90% Ontsira palliatus has great capabilities of looking for host, spreading over rapidly and controlling hosts on a large scale. Therefore, it is much better to adopt the above mentioned parasitic wasp as a biological control agent than to use the chemical insecticide of carbofuran for preventing Semanotus sinoauster from China fir woods, Because the former saves a lot of labour, and is simpler and more effective than the latter.