The　photocatalytic　degradation　of　several　organic　compounds　in　airstreams　was　studied　at　room　temperature　by　using　a　bed　reactor　packed　with　the　commercial　HZSM-5　and　operated　in　a　circulating　mode.　It　was　found　that　the　raw　HZSM-5　shows　an　unanticipated　photocatalytic　activity　for　oxidating　ethylene,　bromomethane　and　methyl　orange.　XRF　and　AAS　analyses　reveal　that　the　photocatalytic　activity　of　the　ZSM-5　results　from　the　trace　amount　of　iron　impurity　in　the　sample,　and　the　photoactivity　is　positively　related　with　the　content　of　iron.　The　primary　results　of　characterization　by　XRD,　DRS,　XPS　and　SPVS　suggest　that　the　most　of　Fe　existed　in　the　framework　of　zeolite　and　in　a　tetrahedral　coordination.　The　iron　species　might　be　excited　by　UV　irradiation　to　form　a　charge　transfer　excited　complex　along　with　the　ligands　and　an　electron　excited　state　of　Fe3+　which　are　responsible　for　the　photocatalytic　behavior　of　zeolites.