Abstract: This paper presents an improved net rewriting system (INRS) -- based method for automatic reconfiguration of Petri net (PN) supervisory controllers for reconfigurable manufacturing systems (RMS) to adapt rapidly to frequent changes in the manufacturing system configurations driven by market changes. INRS addresses the problems of net rewriting systems and can dynamically change the structure of a PN model with preserving its original behavioral properties. An RMS configuration is formally defined by incorporating the formalisms of set and graph. A design method for a class of modular and reconfigurable PN controllers is presented with an approach of INRS. Subsequently, an INRS-based method for automatic reconfiguration of this class of PN controllers is proposed. Using the reconfiguration method, changes in an RMS configuration can be automatically transformed into graph rewriting rules of INRS; by applying the rules to the existing controller, it will be reconfigured into the needed one. The resultant PN controllers obtained by both the design and reconfiguration methods are guaranteed to be valid in theory, without the need of verification. Simulation results show the validity of the presented methods.