This study evaluated the effect of designated smoking areas in an office and the efficacy of air cleaners in a smoking room. The concentrations of suspended particulates (SP) were measured at 13 points in the office, including the smoking room, corridors around the smoking room, and a non-smoking office. The SP concentrations were between 0.52 to 1.31 mg/m3 in the smoking room, 0.06 to 0.22 mg/m3 in the corridors and 0.03 to 0.05 mg/m3 in the non-smoking office, respectively. The results showed that the area restriction on smoking in this office was successful, although an outflow of tobacco smoke was observed in the corridors. The SP concentration in the smoking room where three electrostatic air cleaners had been installed was monitored over 24 hours. The SP concentration due to tobacco smoke in the smoking room was much greater than the control concentration of SP in air-conditioned buildings in Japan, that is, not more than 0.15 mg/m3. The effectiveness of electrostatic air cleaners in closed smoking rooms is discussed.