Illitic clay from locality Liepa, Latvia, was investigated using dynamical thermomechanical analysis during the heating and cooling stage of the firing. DTA, TG, TD, XRD and porosimetry were also performed to obtain a wider sight on the processes influencing the elastic properties of clay. The increase of Young’s modulus (YM) at low temperatures was linked to the release of physically bound water. Above 850 °C, bulk density and YM both increased as a consequence of the sintering. Young’s modulus was found to be more sensitive to the progress of sintering compared to dimension changes. YM values continued to increase during cooling until the glass transition temperature was reached. At this temperature, the first micro-cracks caused by the differences in thermal expansion coefficients of the present phases were expected to appear. YM had a sharp V-shape minimum at β → α transition of quartz, which was a result of alternation of the mechanical radial stresses around the quartz grains. When the transition of quartz was completed, YM continued to decrease because microcracks were still being created on the boundaries between different phases. The decrease of YM during cooling from the glass transition temperature down to the room temperature was significant: ~50 % for all firing temperatures and applied isothermal periods.