We investigated the methodology for installing effective smoking rooms in workplaces. It is absolutely necessary to install exhaust ventilation in smoking rooms. There are two bases for deciding the exhaust ventilation rate. The most important is to eliminate the leakage of environmental tobacco smoke (ETS) from the smoking room. An airflow rate of more than 0.2 m/s at the opening of the smoking room is required by the Guidelines for Smoking Control in Workplaces (Ministry of Labour, Welfare and Health) to eliminate the leakage. This ventilation rate is decided by multiplying the opening area by 0.2 m/s. The second important point is to keep the concentration of ETS in the smoking room less than control concentration (0.15 mg/m3). This ventilation rate is decided by dividing the rate of generation of ETS by the control concentration. It is confirmed that an effective smoking room can be installed by following these guidelines. We used real-time monitoring to evaluate the leakage of ETS from the smoking room and the ETS concentration in the smoking room before and after the improvement. It is concluded that real-time monitoring of ETS is a useful method for evaluating the effectiveness of the smoking room.