Air quality studies during a decorating engineering in northern Taiwan were carried out. Sampling was undertaken during the decorating engineering including the dismantling old decorating, water and electrical pipe engineering, tiling engineering, window installation, pre-system furniture installation, flooring engineering, post- system furniture installation and finishing engineering. The levels of carbon monoxide (CO), carbon dioxide (CO2), formaldehyde (HCHO), temperature, relative humidity and bacterial/fungal concentrations were recorded during the decorating engineering. Results show that the averaged CO concentrations ranged from 1.05 to 22.1 ppm during various engineering. The averaged HCHO concentrations ranged from 0.08 to 0.69 ppm and the HCHO increased apparently after system furniture installation. The averaged PM2.5 and PM10 concentrations ranged from 97.2 to 6,445 µg/m3 and 129 to 6,837 µg/m3, respectively. The PM concentrations for the tiling engineering were more than two times of the recommended exposure limit (REL) of respirable particles of 5 mg/m3. The mean respirable fractions, Rb and Rf, for bacteria and fungi, ranged from 27.8%–97.0% and 29.4%–93.8%, respectively. It should be noticeable that over 75% of Rb and Rf were higher than 50% during the decorating engineering. The relatively high respirable fractions of bioaerosols and the high PM concentrations for some specific decorating engineering probably implies a higher adverse health risk for sensitive workers. There are limited information about the air quality for the decorating engineering and this preliminary study can provide references to the Taiwan government on air quality management for workplaces.