In the article are considered structural phase transformations during continuous cooling of medium-carbon steel with different contents of molybdenum and niobium. The features of the phase transformations course during decomposition of austenite depending on the cooling rate are revealed. The structure and microhardness were studied. Continuous cooling transformation (CCT) diagrams are constructed for all studied chemical compositions. The effect of molybdenum and niobium on the kinetics of phase transformations and the hardness of the steels studied are shown.