This article investigates the influence of various parameters of hydrothermal treatment on the properties of lightweight silicate bricks obtained using substandard clay raw materials, construction lime and aluminosilicate microspheres. It was found that it is possible to obtain products with the required performance characteristics at a minimum hydrothermal treatment pressure of 0.2 MPa. With an increase in pressure to 0.4 MPa, it is possible to reduce the time of isothermal exposure while main-taining the required properties, which helps to reduce the energy intensity of production. The optimal amount of CaO depends on the specific parameters of hydrothermal treatment. So in order to achieve maximum strength indicators, the content of CaO is 10 wt. % at a pressure of 0.2 MPa and 15 wt. % at a pressure of 0.4 MPa, respectively. The addition of aluminosilicate microspheres makes it possible to significantly reduce the average density and obtain a lightweight silicate brick with this indicator from 930 to 1610 kg /m3. The rational time of isothermal exposure, ensuring the formation of a cementing compound of optimal composition, and as a result, obtaining a material with high physical and me-chanical properties at a pressure of 0.2 MPa is 8 hours, and at a pressure of 0.4 MPa is 6 hours. Math-ematical models are proposed for the selection and optimization of lightweight silicate brick compositions based on construction lime, substandard clay rocks and aluminosilicate microspheres.