Inertial impactors have been used widely to measure particle size distribution, analyze chemical composition, and obtain aerosol sampling. Conventional impactors have particle-surface interaction problems. These problems reduced separation efficiency. To enhance separation efficiency. it is desirable that surface is coated. But coated surface has significant problem in high temperature environment and bio aerosol sampling. The cavity impactor that is not a conventional design can be used in such situations. The efficiency of a conventional impactor and the cavity impactor was investigated for different Reynolds numbers in this paper. 50% cut-off aerodynamic particle diameter was smaller in the cavity impactor than in the conventional impactor because of flow direction change. Fine particle contamination and reentrainment were reduced in the cavity impactor.