Hardness, electric conductivity and saturation magnetization measurements were used to study phase transformations in a maraging steel close in composition to the steel type 20Kh2N4M2FSYu during isochronous tempering with successive temperature increase within 75-670° C range and isothermal ageing at 470° C. A number of model steels was also investigated to divide and analyze two main strengthening mechanisms: carbide and intermetallic precipitation. It was shown that the properties of maraging steel after tempering were conditioned by superposition of two above-mentioned processes. A particular attention was given to the role of molybdenum and to reversibility of intermetallic ageing.