<p>The Raniganj basin in India offers significant potential for underground coal gasification (UCG), a process in which coal seams are heated to produce syngas. However, this technique can induce thermal stress in the surrounding sandstones and shale, increasing the risks of land subsidence. To better understand how sandstones behave under UCG conditions, three types of sandstones—fine, medium, and coarse—were collected from the Raniganj coal basin. These samples, each with distinct chemical compositions, were subjected to varying thermal treatment temperatures (T_T) (25–900&#xa0;°C). The study measured the sensitivity of several thermo-mechanical properties, including bulk density (<i>ρ</i>), effective porosity (<i>ϕ</i>), P-wave velocity (<i>V</i>_<i>P</i>), Young’s modulus (<i>E</i>), Poisson’s ratio (<i>ν</i>), and Brazilian tensile strength (BTS), to temperature changes. The findings indicated that each sandstone type exhibited unique characteristics, which were normalized and plotted against the thermal treatment temperature. Overall and individual regression equations were developed for each property to estimate normalized values at different temperatures. The regressions for individual sandstones performed much better than the overall regression model. Four zones were identified depending on the thermal response of sandstones (Zone I: Desorption, Zone II: Thermal expansion, Zone III: Clay decomposition quartz transition, and Zone IV: Calcite decomposition). The results revealed that in Zone III, the fine, medium, and coarse sandstone exhibited a 31.6, 46.06, and 67.05% reduction in BTS, respectively, indicating pronounced structural damage due to the <i>α</i>-to <i>β</i>-quartz transition. Additionally, medium and coarse sandstones, which contain carbonate minerals, were found to be more sensitive to thermal treatment compared to fine sandstones lacking carbonate minerals.</p>