This study selected 21 representative public sites for the survey of indoor air quality in Tainan area, including hospital, school, fitness center, government office, library, theater, transport station, and supermarket. Indoor air quality was first assessed by direct detection apparatus, including CO2, CO, HCHO, TVOCs, bacteria, fungi, PM10, PM2.5, O3 and temperature. Based on the results of walk-through detection, the spatial distribution of indoor air contaminants was further measured in a 24 hour period by the EPA standard method. The detailed measurements illustrated HCHO, O3, PM10 and PM2.5 concentrations are lower than the suggested threshold levels in all public sites. CO2 concentrations at hospitals and school are all exceeding category 1 threshold of 600 ppm. Bacteria exceeding the suggested threshold of 500 CFU/m3 for category 1 and 1000 CFU/m3 for category 2 is popular at most public sites. One fitness center was found exceeding the TVOCs threshold of 3 ppm, and outdoor air can be a potential source. The high levels of CO2 and bacteria were a common indoor air quality problem, and the regulated strategy of crowd control and air conditioning management was required for a healthy indoor environment.