Lim et al. reported that the indirect contributions(synergy effect) of photo-catalytic process from the hybrid system composed of UV/photo-catalytic reactor and a biofilter were four times as much as its direct contributions ot the elimination cpacity of toluene as well as ethanol from waste-air. As a control Lim et al. observed the transient behavior of semi-pilot scaled biofilter to treat waste air comtaining both hydrogen sulfide and ammonia. In this paper the time-dependent behavior of semi-pilot scaled hybrid system composed of UV/photo-catalytic reactor and a biofilter was observed for the simultaneous treatment of hydrogen sulfide and ammonia, compared with the previous result of Lim et al.. The removal efficiencies of hydrogen sulfide and ammonia for the hybrid system turned out to be ca. 83% and ca. 65%, respectively, which were improved better by a few percent and 30%, respectively. Thus the hybrid system composed of UV/photo-catalytic reactor and a biofilter contributed to the enhancement of the removal efficiency of ammonia more than to that of hydrogen sulfide.