The exhaled radon originated from building materials corresponds to the indoor radon activity concentration. One of the most commonly used building materials is the brick made from clay by heat treatment. In this study, the radon emanation and radon exhalation features of clay samples are presented as a function of heat applied (100-950°C). The free radon exhalation was determined with the help of radon accumulation kit. The initial radon exhalation value continuously reduced owing to the increased temperature. In the case of the highest temperature treated sample, the measured exhalation was <1 % of the original. The tendency of the loss relates to the internal structure modification, which was also investigated (porosity, specific surface and superficial morphology by environmental scanning electron microscope snapshots). On the basis of the obtained result, it can be safely stated that strong correlation can be observed between the internal structural changes and the found exhalation profile.