During surface hardening of steels using pulsed laser sources, rapid thermal changes are imposed on the material. These changes yield locally different austenitizing and hardening conditions in the laser-affected zone driven by the thermal conductivity and transformation behaviour of the material. The hardened surfaces are characterized systematically by a depth-resolved analysis of X-ray interference lines. A diffractometer with CoK alpha -radiation is used to determine the halfwidth, the state of residual micro stress and the dislocation density in the laser-hardened zone. The X-ray characterization is accompanied by investigations in micro hardness, light and electron microscopy. Characteristic profiles of different microstructural parameters are obtained along the laser hardened zone. Specimens made of two different steels with similar contents of carbon and different contents of carbide forming elements are laser treated by a temperature controlled pulsed solid state laser. Especially designed specimens are used to reproduce the effects of the pulsation without the influence of the feed. The influence of frequency and duration of the laser hardening process are investigated separately. Additionally, investigations on specimens with different preceding heat treatments are carried out.