In order to obtain a better understanding of the intentional thermal alteration of Palaeolithic materials in the northeastern region of Japan, heating experiments were carried out on two types of shale samples. Mechanical properties such as strength and hardness as well as surface morphology were analyzed before and after heating. As a result, a functional change was observed in mechanical factors after heating. A hard shale sample comprising small grains exhibited a significant decrease in strength and noticeable increase in hardness after heating. On the other hand, shale comprising larger crystal grains exhibited an increase in both strength and hardness values. Moreover, smoother surfaces were observed through SEM analysis in both samples after heating. These results lead us to the conclusion that the heating process, especially in the case of harder shale with higher strength values, might have modified material properties such as flaking characteristics as well as functional attributes that are relevant to hardness.