In this paper, we present an extended fuzzy Petri net model (EFPN) for modeling fuzzy IF-THEN rules and fuzzy IF-THEN-ELSE rules of a rule-based system, where the truth values of the propositions appearing in the rules are represented by vague values in [0, 1]. An efficient algorithm is also proposed to perform vague reasoning automatically. This vague reasoning capability allows computers to perform reasoning in a more flexible and more intelligent manner.