Objective: The objective is to determine if aerobic and anaerobic sampling yields viable biologic contaminants in the aluminum oxide air abrasion powder as delivered by the manufacturer and to determine mean particle size for comparison with the published size from manufacturers and the range of sizes in the powders. Method and materials: Samples from 15 unopened aluminum oxide powder containers from 9 different manufacturers were plated on aerobic and anaerobic culture media. The cultures were incubated at 35°C and observed at 24-hour intervals. Samples of each of the 15 groups were subjected to scanning electron microscope (SEM) examination. Photomicrographs were obtained and a range and mean particle size determined. Results: Aerobic and anaerobic cultures demonstrated no growth in any of the samples. Mean particle size determined by SEM for 25- to 27.5-µm particles ranged from 27.3 µm to 32.0 µm with standard deviations from 1.06 µm to 7.70 µm. Mean particle size for 50 µm particles ranged from 51.6 µm to 59.7 µm with standard deviations of 5.48 µm to 14.80 µm. Conclusion: Aluminum oxide powders as delivered by manufacturers appeared to be free from viable microorganisms. The powder mean particle sizes approximate the labeled sizes closely enough such that they should perform properly in air abrasion tooth preparation.