A batch control system consists of several components which run in parallel and influence each ether. To reduce system design complexity, a modular approach is useful, in which the whole system is designed by composing subsystems (modules) designed independently. In this paper, we propose a modular design approach for the synthesis of sequential control systems. Sequential control systems are modeled by condition/event nets, and their behaviors are described by partial languages. We also present a method of constructing sequential controllers from condition/event net system models.