A hot forging of steel usually consists of buster, blocker and finisher processes. The blocker is a transient shape to ease the metal flow in the finisher dies and it is designed by experienced engineers with rules. Re­cently, due to the lack of such engineers, it is necessary to develop an expert system to automate the design operations. In the present study, a rule-based expert system was developed for the blocker design of ax­isymmetric hot steel forging. In this paper, the major rules used in the system are summarized and the designed blockers were verified by rigid thermoviscoplastic finite element method.