The main objective of the project is to develop an expert system on process planning regarding to the prismatic parts by using a commercial expert system development tool, KES (Knowledge Engineering System Shell). The system is a generative type of CAPP system which used feature description approach as the input format. The process knowledge of the system is organized in modular form in order to ease its system development and also future enhancement. Furthermore, the knowledge bases are embedded with C language for the purpose of achieving a more versatile expert system. The output of the system is a process planning sheet which contains the recommended stock material size, machining operations, cutting tools, machines, spindle speeds and feedrates.