Abstract: Suspicious aerosol samples need to be pretreated for detailed analysis in radionuclide monitoring proposed by the Comprehensive Nuclear-Test-Ban Treaty (CTBT). These samples are quite different from common aerosol samples since their filter matrix are massive and the number of analysed elements is large and their contents are very different. As a result, any single pretreatment method is not effective for recovering all radionuclides. A novel extraction-ashing-digestion method is proposed in this paper, including microwave extraction of volatilizable radionuclides, ashing of filter matrix and microwave digestion of difficultly soluble radionuclides. The spiked samples with polypropylene fibrous filter matrix were prepared. Natural abundance elements cesium, cerium and zirconium were selected as trace elements to validate the method. The recoveries under varied conditions such as pressure, power, duration time of microwave extraction, ashing temperature and time, as well as composition and concentration of microwave digestion reagents, were studied experimentally. The results show that cesium, cerium and zirconium in samples can be recovered completely under the optimum conditions.