Experiments were conducted to compare the annealing of nano-porous aluminum oxide membranes by 2.45 GHz microwave radiation and by conventional (resistive element) furnace heating. The starting material was , membranes that were 60μm thick, 13mm in diameter, and containing pores of approximately 200nm diameter. Changes in the porosity and morphol­ogy were recorded from digital processing of scanning electron microscope (SEM) images. The data indicates that both microwave and conventionally-heated annealing resulted in a decrease of surface porosity and an apparent increase in the number of pores. However, microwave annealing consistently resulted in a 4-5% greater reduction in porosity and a greater increase in the number of (small) pores than conventionally-heated annealing. These results are consistent with a non­thermal mechanism for microwave-enhanced surface diffusion, although the complex morphology of the pores precluded a quantitative theoretical analysis.