The purpose of this study is to construct an expert system for mold polishing using knowledge of skilled machinists and to verify the feasibility of the expert system with experiments. In the first report of this theme, these knowledge have been acquired and analyzed quantitatively. In this expert system, production rule is used to express the knowledges. If the roughnesses and depth of scratches of preworked surface and required one are given, then order of tools to be used and number of each polishing stroke are obtained as solution. Inference engine is forward inference of production rule and the criterion of evaluation is minimum number of total polishing strokes. According to the solution of this expert system, milled surface of S 55 C steel are polished with selected tools and the number of polishing strokes. Consequently, the expert system is confirmed to be useful for determination of polishing process.