This paper presents a production scheduling system for batch reactors using Constraint Logic Programming (CLP). To keep the productivity of a plant high, it is necessary to make up a proper production plan. Because the re-scheduling is repeated frequently during the scheduling horizon, as customers change or cancel their orders, it is sufficient to organize an improved feasible plan instead of the optimal one. To computerize this process, various problems need to be solved. First, the scheduling process should be formulated. Computation should be fast, since the customer's demands arise suddenly and a quick response is needed. The main benefit of this system is to save man-power for scheduling and to realize better order fulfillment, such as keeping the deadlines of deliveries. Once computerized scheduling is introduced, the expert planner who engages in a current scheduling work of production without a computer will be released from this daily routine work, and also anyone in the plant will be able to make up an appropriate production plan of the same quality with this system. CLP is a useful tool to solve the combinatorial problem, which enables us to consider several difficult constraints easily. In this paper, the outline of this system is explained, then the result and the effectiveness of applying this system to batch reactors in a real plant are presented through an example.