The elastic moduli, i.e., Young's modulus, shear modulus and Poisson's ratio, of a sintered La0.9Sr0.1Ga0.8Mg0.2O3-delta bulk have been experimentally determined in the temperature range from room temperature to 1373 K using a resonance technique. Anomalous elastic properties were observed over a wide temperature range from 473 to H 73 K. In the results for internal friction and in X-ray diffraction measurements at elevated temperature, two varieties of structural changes were seen in La0.9Sr0.1Ga0.8Mg0.2O3-delta in the examined temperature range. The results agreed with the findings of a previous crystallographic study of the same composition system by Slater et al. In addition, the temperature range in which a successive structural change occurred in La0.9Sr0.1Ga0.8Mg0.2O3-delta was the same as that exhibiting the anomalous elastic properties. Taking all the results together, it can be inferred that the successive structural change in the significant temperature range is responsible for the elastic property anomaly of La0.9Sr0.1Ga0.8Mg0.2O3-delta. (C) 2004 Elsevier B.V. All rights reserved.