Transient behavior of biofilter/photo-catalytic reactor system was observed to eliminate hydrogen sulfide from waste air at its four sampling ports. The biofilter was packed with a eqivolume mixture of granular activated carbon(GAC) and compost as packing media on which Thiobacillus sp. IW was inoculated and was fixed. The biofilter/photo-catalytic reactor system was run for eight stages of operation under various operating conditions. As a result the removal efficiency began to decrease from 100% after the inlet load of hydrogen sulfide surpassed ca. 100 S-g/m3/h and was finally continued at 60%. The maximum elimination capacity of biofilter/photo-catalytic reactor system was ca. 130 S-g/m3/h.