In the time of energy saving different methods of thermo insulation have been developed and one of them besides the comprehensive use of thermo insulation materials is use of masonry consisting of aerated concrete blocks. In order to determine the contribution of aerated concrete in total scope of heat insulation it is important to determine the distribution of humidity in the wall construction itself. One of non-destructive methods for determination of humidity level and its distribution throughout the aerated concrete constructions is application of electrical impedance spectrometry. In laboratorial test series it is detected that within increasing of the humidity level in aerated concrete block the electrical impedance of the construction decreases. Using this method it is possible to detect the distribution of humidity throughout the construction in relative means. If absolute means are important, then calibration work must be performed prior field testing. In order to increase accuracy of the results obtained, the frequency analysis must be performed for every type of testing material. In this paper non destructive testing of a wall segment from aerated concrete blocks is described in order to determine the distribution of humidity level throughout the section of the blocks during the drying process of the construction. The frequency analysis and impact of irregularities in structure for aerated concrete blocks is described as well.