CO2 laser cutting of steel sheets is considered and influence of beam waist position relative to the workpiece surface and the workpiece thickness on the striation formation is examined. The kerf width is modeled using a lump parameter analysis. The measurements are composed with the experimental findings. SEM and optical microscopy are conducted to examine the cutting surfaces. It is found that beam waist position has significant effect on the kerf size and as the workpiece thickness reduces, the relative location of beam waist position varies for the minimum kerf width. The microcracks are found in the resolidified material at the cutting surface, which is due to non-uniform and rapid cooling of the resolidified material at the surface. (c) 2005 Elsevier B.V. All rights reserved.