This paper deals with the identification of multidomain configuration in ferroelastic phases of La0.95Sr0.05Ga0.9Mg0.1O3−x using polychromatic synchrotron X-ray radiation (Laue method). A nonde-structive approach for the determination of domain misorientations, orientation of domain walls and theirconfiguration in the nanosize ferroelastic domain structure was developed. The proposed approach can be used tostudy the nanosize ferroelastic domain structure in small crystals of submillimeter sizes at different external fields,including temperature. The ferroelastic domain structure in the orthorhombic as well as in the rhombohedralphases of La0.95Sr0.05Ga0.9Mg0.1O3−x crystals has been identified. The intersection of walls leads to the formationof a chevron-like pattern. The observed reversibility of domain patterns during temperature cycles is probablycaused by the interaction of domain boundaries with point defects, most likely oxygen vacancies.