The concept of oxidizing diesel soot in a microwave-assisted catalytic trap was demonstrated. Comparisons were made to experiments using electric heating with and without catalysts to understand the influence of microwave irradiation on catalysis. The complex permittivities of the three materials (diesel soot, catalyst and support) involved in such a system were measured and the feasibility of using this combination of materials in diesel soot burn-off was evaluated, based upon these measured data. It was found that iron and copper were the most active catalysts in lowering the ignition temperature of diesel soots, while palladium was a necessary component in achieving more complete combustion. The iron-containing catalyst was also very effective and energy-efficient at low microwave input. A non-thermal or microwave enhancement effect was observed which further decreased the ignition temperature by more than 200 degrees C. It was also found that the more vigorous burning of diesel soot by microwave heating led to an increase in carbon monoxide in the combustion products, because of the difference in the heating mechanism. However, when palladium was used, the same completeness of combustion as in electric heating could be achieved.