Powdered black pepper with varying moisture contents were subjected to intermittent or continuous microwave treatments (2450 +/- 50 MHz, 450 Watt) for 50 or 150 sec. Microwave treatment reduced microbial load in all treated samples. Higher product moisture and prolonged treatment time resulted in higher microbial reductions. The highest microbial reduction was in the groups, to which microwave treatment was applied continuously for 150 sec. Compared to the untreated samples in this group, the counts of total aerobic mesophilic microorganisms, Enterobacteriaceae, and yeast and mould were reduced by 87.8, 94.9 and 90.7%, respectively. However, in all the treated groups, the losses of volatile oil were between 3.9 and 18.7%. The results indicated that microwave treatment caused microbial reductions in the powdered black pepper, although the reductions were unsatisfactory. The levels of the reduction depended on the moisture content of the samples and exposure time. The losses of volatile oils occurred during the process were in acceptable levels.