Direct visualization of rare earths in alpha- and beta-SiAlON unit-cells is performed through Z-contrast imaging technique in an aberration-corrected scanning transmission electron microscope. The preferential occupation of Yb and Ce atoms in different interstitial locations of beta-SiAlON lattice is demonstrated, yielding higher solubility for Yb than Ce. The triangular-like host sites in alpha-SiAlON unit cell accommodate more Ce atoms than hexagonal sites in beta-SiAlON. We think that our results will be applicable as guidelines for many kinds of rare-earth-doped materials. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.