The high-temperature behaviour of a feldspar group mineral, filatovite (with the simplified formula: K(Al,Zn)2(As,Si)2O8), in which the Al:As:Si ratio is close to 2:1:1, was studied by in situ high-temperature single-crystal X-ray diffraction and in situ high-temperature (hot stage) Raman spectroscopy up to 600 °C. In the temperature range studied (25–600 ºС) filatovite does not undergo any phase transition, whereas at 800 °C it decomposes to X-ray amorphous phase(s). The evolution of twelve main Raman bands was traced during heating, which indicates a gradual change in the crystal structure. The thermal expansion coefficients (TECs) of filatovite demonstrate a sharply anisotropic character of thermal expansion: the maximal expansion is close to the a axis (α11 = 17.7(1) × 106 °C–1), whereas along the b and c axes the TECs are close to zero. Such behavior is typical for the minerals with a similar crystal structure topology; it indicates the dominant role of structure geometry in the thermal behavior of the mineral.