In this study, we investigated the temperature dependence of magnetostriction in the twinned rhombohedral perovskite structure-based lanthanum cobaltite La0.8Sr0.2CoO3. The magnetostriction measured in a magnetic field applied along the pseudocubic [111](c) axis showed large hysteresis and residual strains. The residual strains are caused by the twin deformation, which we observed using x-ray diffraction. We found that the critical magnetic field for the twin deformation of La0.8Sr0.2CoO3 increases with temperature. The twin deformation occurs in a sufficiently strong magnetic field (similar to 6 T), even in the paramagnetic region at room temperature. We also confirmed that the temperature dependence of the critical magnetic field for twin deformation is related to the temperature dependence of the magnetization. (c) 2020 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).