A Q-switched Nd:YAG laser was used in the laser marking process of stainless steel. The influence of the pulse frequency of the laser beam on the mark depth, width and mark contrast have been studied in this paper. The mark contrast is the ratio of the apparent brightness between the mark and unmarked areas which shows the clearance degree of the mark. An optical microscope, scanning electron microscope and surface profile instrument were used to measure the effects of pulse frequency on the mark depth and width. An image-analysis system with a frame-grabber card and a charged-couple-device (CCD) was used to measure mark contrast. It has been found that the mark depth, width and mark contrast depend on the interaction process of the laser beam and the material, which was influenced dramatically by the pulse frequency. The pulse frequency of the laser has a significant effect on the mark quality. There is maximum mark depth when the pulse frequency is about 3 kHz, while mark width almost keeps constant at different pulse frequency. With the pulse frequency increasing, evaporation of material becomes less, and at the same time oxidization becomes more significant, which leads to the improvement of mark contrast. The highest mark contrast could be obtained when the pulse frequency of laser was about 8 kHz. © 2003 Elsevier Science B.V. All rights reserved.