A carbon dioxide laser with a power of 1.5 kW was employed for surface hardening of a hypoeutectoid Ck-60 steel. The microstructures and hardness profiles were determined as a function of power density and laser beam travel speed. The microstructure in the laser-beam hardened zone depended on power density and consisted of plate martensite (for high power density) or autotempered martensite (for low power density). In the transition zone of the laser-beam treated specimens, martensite and ferrite were observed. Case depth and maximum hardness were found to depend on power density and travel speed. A simple one-dimensional heat flow model has been used for the selection of process parameters and for the prediction of case depth. Calculated and experimentally determined case depths are in good agreement for medium values of power density.