The VOCs have a direct influence on indoor air pollution, and stimulate respiratory organs and eyes in human body. Also, most of VOCs are a carcinogenic substances and causes to SBS (sickness building syndrome). Therefore, this study was progressed in photocatalysis of VOCs using UV/$TiO_2$ which was a benign process environmentally. The experiments were performed to know photodegradation characteristics as crystalline structure of $TiO_2$ which had anatase, rutile and P-25 (anatase : rutile = 70 : 30). The main purpose of this study was to identify photocatalytic characteristics as inlet concentration of reactants, $H_2O$, and residence time.