In recent years, the notion of the expert system (ES) has become very popular, and its enormous potential to industry and ways in which it could improve decision-making have been recognized. This article presents the research work of an expert system (ESIMCOST) the authors developed to assist the manufacturers in the injection mold cost estimation at the early product design stage. The system domain is concerned with the concurrent decision-making of the plastic part design, injection mold design, and mold-making process planning during the cost estimation process. Numerous interrelated variables and technical data for estimating the injection mold cost are well organized. With the inputs of the features of a plastic part, the ESIMCOST will generate an estimated cost of the injection mold required to produce the part. Some of the projected benefits from the system implementation are addressed in the article.