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.