In the present study, high-power laser cutting of steel sheets is considered and the influence of the workpiece thickness and the laser frequency (laser pulse repetition rate) on the resulting cutting quality is examined. The laser-cutting quality is assessed by measuring the out-of-flatness of the cut edges and the dross height at the cut edges. An experiment is carried out to cut the steel sheets using the CO2 laser. The optical microscope is used to measure the geometric features of the cut sections for the quality assessment. It is found that workpiece thickness has significant effect on the resulting cut quality. In this case, increasing workpiece thickness lowers the cutting quality through enhancing the sideways burning. Moreover, the laser pulse frequency has less influence on the cutting quality as compared to that corresponding to the workpiece thickness.