Rock masses typically contain joints and defects affecting their safety and stability under compression, shear, or tension. The shear strength of these discontinuities, influenced by environmental factors like temperature, is critical in deep rock engineering. This study conducted direct shear tests on sandstone joints at room temperature (RT) and after thermal treatment at 250 °C and 500 °C. The behavior under compressive and shear forces was investigated by using the direct shear test. The results showed that compressive and shear properties improved at 250 °C but deteriorated following thermal treatment at 500 °C. Peak shear strength before and after thermal treatment closely followed Patton's bilinear failure criterion. As intact asperities were sheared under normal stress of 0.75MPa, the residual shear strength was less affected by temperature than peak shear strength. The shear strength of intact asperities increased by 8.8% following thermal treatment at 250 °C and decreased by 4.3% at 500 °C. The joint closure, normal stress, and stiffness were consistent with a modified Bandis et al. (1983) criterion. Increasing the thermal treatment temperature from RT to 250 °C and 500 °C changed maximum joint closure from 0.201 to 0.125and 0.301 mm, and subsequently, the initial normal stiffness from 8 to 19.6 and 6.62MPa/mm, respectively. These findings offer valuable insights into the temperature-dependent behavior of sandstone joints, aiding the design and maintenance of deep underground structures. This research is particularly relevant to engineering geology, where understanding the thermo-mechanical behavior of rock joints is essential for projects such as geothermal energy extraction and the storage of nuclear waste. The results can improve the safety and efficiency of geological engineering practices in thermally active environments.