Problems with environmental tobacco smoke to be called ETS in this presentation have become a cause for widespread concern and restrictions on smoking in public spaces have become common place. The problem of ETS may be reduced significantly if there is a sufficient ventilation system in place. Commercial airplane cabins are divided into smoking and non-smoking sections and this has caused some problems. The environment around the "Common Smoking Seats" located at the left side end of the cabin is one of them. "Common Smoking Seats" are left available to smokers who have to sit in non-smoking seats, as long as two seats are vacant in economy compartments. The authors developed a new ventilation system to improve the environment around these seats. The new system has been developed after conducting several measurements of air flow pattern and calculating the velocity distribution through numerical simulation in cooperation with Japan Tobacco Inc. and Japan Airlines. The system has two smoking seats back-to-back with the seats positioned near the stern of the airplane and there is a special grill on each nozzle to regulate the supply airflow directions. Numerical simulation indicated that one smoking seat could be located at the left-hand side end and an other at the right-hand side and the optimum angle of the supply airflow directions. After the introduction of this system on international Boeing 747-400 of Japan Airlines, the environment around these "Common Smoking Seats" was remarkably improved.