For a certain period of time in the production of aerated autoclaved concrete [AAC] the addition of gypsum, as an additive which accelerate the tobermorite formation in this concrete is used. However, there is no data concerning the influence of tobermorite on the properties of AAC, even on the strength. The paper is devoted to the effect of replacing gypsum by limestone meal on the properties of AAC. The addition of limestone was the same as gypsum i.e. 10 kg/m3 of concrete. The sand technology was used. From the results of experiments the following conclusions can be drawn. The limestone meal is a very interesting mineral additive, which principally the higher degree of quartz participation in the hydrates formation during autoclav ing is giving. The mechanism is the quartz participating in the scawtite crystallization. As it is well known the gypsum addition the increase of tobermorite formation is causing. However, to obtain more information on the properties of AAC, principally about strength and thermal conductivity, the larger samples should be examined. thus the industrial trials are needed.