In time of energy saving it is important to monitor humidity migration process through delimiting constructions. Autoclaved aerated concrete (AAC) is considered to be one of the most efficient load bearing construction materials in aspect of thermo insulation. For AAC it is important to determine the distribution of humidity throughout the cross section of the construction because it influences the thermic resistance of the construction. Therefore, it is important to monitor the drying process of AAC masonry constructions. This aim can be reached by non-destructive testing methods, which are easily applicable on inhabited buildings as well as on buildings, which are in construction phase. One of such methods is electrical impedance spectrometry (EIS), which can be used for determining of humidity distribution throughout the cross section of the construction. For this non-destructive testing method, it is important to choose correct measurement frequency in order to obtain credible results of humidity distribution. In this paper, methods of choosing suitable measurement frequencies are described as well as impact of different factors on choosing of the most suitable measurement frequencies of AAC masonry constructions.