Abstract An increased interest in vacuum carburizing concept is being observed in the last years all around the world as a result of the progress in designing of modern furnaces for thermo-chemical treatment under low pressure and of better knowledge of physico-chemistry of these processes. This in turn allows a precise control with aid of computer simulations. The vacuum carburizing simulation programs allow selection of optimal process parameters to obtain pre-determined carbon concentration profile in surface layer at a time as short as possible. These objectives are being achieved as a result of better knowledge about surface phenomena occurring during vacuum carburizing process.