Process parameters in microcutting are controllable comparing to other dynamically varied factors affecting the micromachining processes. Based on the Taguchi method, the three key process parameters of the axial depth of cut, the radial depth of cut, and the feed in micromilling of very important engineering material brass H68 are experimentally studied in an orthogonal way on a micromilling machine tool with submicron accuracy. The achieved surface roughness in micromilling experiments are used as the evaluation criterion. The extreme difference analysis and the variance analysis of the experimental results have identified the affecting tendencies of the three key process parameters on the final micromilling results. It turns out that the radial depth of cut affects the finished surface roughness most greatly in micromilling of brass H68. The feed and the radial depth of cut have significance on the surface roughness.