This study is an investigation of the effect of high temperatures on the engineering properties of sandstone. The rock was first subjected to a range of temperatures such as 25 °C, 200 °C, 400 °C, 600 °C and 800 °C, and a series of porosity, unconfined compression, X-ray diffraction and scanning electron microscope tests were then performed on the heated specimens. In addition, sandstone specimens were also subjected to different numbers (i.e. 1, 2, 4, 6 and 10) of thermal cycles to better understand the effect of high temperature variations on rock behaviour. It was observed that high temperature in the range of 200–400 °C had some influence on the rock properties; that is, the porosity slightly decreased while the strength of the rock increased. However, for T ≥ 600 °C, there was a significant increase in rock porosity that correlated with a decrease in rock strength. The observed changes in engineering properties were attributed to the changes in rock mineralogy and microstructure that occurred at T > 600 °C where the major minerals underwent the process of phase transformation and a significant increase in rock cracking. Regardless of the temperature, almost all specimens failed in tension during unconfined compression. The effect of thermal cycles was seen in a progressive increase in rock porosity and a corresponding decrease in the elastic modulus of the rock.