Nowadays, there are more and more attempts to replace cement with some kind of suitable pozzolana. Thermally activated clays have become the favoured materials in this field. However, the investigated clays are generally pure kaolinite or kaolinitic clays. This article is aimed at the possibility of thermal activation of brick soils, more specifically of those materials with only about 30-65% of clay minerals. Brick soils from three different localities have been examined. With the help of simultaneous thermal analysis, four temperatures for thermal activation were established, namely 550°C, 600°C, 650°C, and 800°C. Mechanical properties revealed the promising performance of brick soils calcined at 650°C. Especially, the one with a high calcite content reached even higher compressive strength than calcined kaolinitic clay. The pozzolanic activity of activated brick soils was confirmed by measuring the heat flows in the mixture with lime.