This study investigated the effect of smoking on Indoor Air Quality in smoking allowed buildings. Total 26 buildings(Restaurants 3, Billiards 4, Karaokes 6, Golfs 7, Pubs 6) were surveyed for nicotine, PM10, CO2, CO, NO2, HCHO, TVOCs, benzene, toluene, ethylbenzene, styrene and xylene at quiet and busy time, respectively. The concentrations of nicotine, PM10, CO2 and benzene were significantly higher(p<0.05) at busy time compared to the quiet time. Some buildings exceeded Indoor Air Quality Standards for PM10, CO2, HCHO and TVOCs. Our results show that smoking-ban legistration should be introduced to improve Indoor Air Quality. Keywords : Smoking, Indoor Air Quality, Nicotine, Smoking-Ban Legistration.