High-resolution solid-state 27Al NMR spectra have been obtained from ALON, β′-sialon and yttrium aluminate phases. The usefulness of 27Al magic-angle spinning NMR in phase characterization is shown by comparing different preparations of the yttrium aluminates. The sensitivity of the 27Al resonance position to the local environment means different units (e.g. AlN4, AlO4, AlO6) can readily be distinguished allowing oxynitride structures, containing elements of similar scattering factor, to be refined. This is exemplified for the β′-sialon phase. For quadrupolar nuclei (nuclear spin, I≥ 1) such as 27Al (I =), interaction with the local electric field gradient can cause extensive broadening of the resonance such that the NMR spectrum may not precisely quantify the aluminium distribution. © 1988, Wiley-Blackwell. All rights reserved.