The optimal temperature control of a batch jacketed free radical polymerization reactor by fuzzy control method with genetic algorithm (GA) is considered. The manipulated variable was chosen as the heat given by the immersed heater. A key issue in this study is to generate sets of fuzzy control membership function and relation matrix using GA, which can be easily implemented and an efficient method for optimization problems. The fitness function for GA is chosen as the integral of the absolute value of error (IAE). By using the fuzzy parameters obtained for three different optimal temperature profiles, the efficiency of the fuzzy controller with GA was examined by simulation and experimentally. It was seen that GA is able to tune the fuzzy controller efficiently for different situations and therefore to control the temperature of the polymerization reactor. (C) 2003 Elsevier Science Ltd. All rights reserved.