|In this paper, we propose a genetic algorithm for dealing with preemptive job shop scheduling problem. The proposed algorithm considers constraint-based algorithm for preemptive scheduling problems. We apply a genetic algorithm to these problems. For preemptive job shop scheduling problems, we develop a new genetic representation, a new crossover and mutation method. We also incorporate a conventional heuristic rule (i.e., shortest processing time rule) into the proposed genetic algorithm. In case study, we supply the proposed algorithm to several job problems. Experiment results show that the proposed algorithm outperforms the conventional algorithms.