In this work, measurements of the thermal properties of moist autoclaved aerated concrete specimens have been performed using both the heat flow meter apparatus (HFM) and the transient plane source technique Hot Disk (TPS). When testing moist materials, the steady-state condition can take a long time to be reached; furthermore, an additional difficulty occurs, because the temperature gradients inside the material cause a moisture transport with a moisture redistribution and a latent heat due to phase change. Therefore, for a correct determination of the thermal conductivity, it is necessary to separate these effects from the measurements. The transient plane source technique Hot Disk is a transient technique which carries out measurements in few seconds to make negligible the moisture redistribution; on the contrary, using the heat flow meter apparatus the steady-state condition is reached only when there is a total redistribution of the moisture contained in the specimen. Measurement data obtained from these two different methods (HFM and TPS) have been analyzed and compared; only in this way it was possible to perform an accurate computation of the moisture conversion coefficient of the thermal conductivity according to the EN 10456.