Clay brick was perhaps to be the first artificial structural material. First bricks were dried by sun; later people had started to burn bricks by fire and in that time further enhancements appeared. This article deals with two kinds of fired clay bricks; basic physical properties, pore system characteristics and thermal properties are studied. The values of basic physical properties by water vacuum saturation vary slightly; bulk density shows values around 1880 kg/m³ and in the case of open porosity it is around 27%. Regarding thermal properties the difference is higher, obtained results of thermal conductivities in dried state vary by about 33%.