This　study　investigated　the　chemical　nature　of　impurity　iron　species　and　photoactive　sites　in　the　commercially　available　HZSM-5　zeolites　with　different　Si/Al　ratios.　The　samples　were　characterized　by　X-ray　fluorescence　spectroscopy,　atomic　absorption　spectroscopy,　X-ray　absorption　near-edge　structure　spectroscopy,　extended　X-ray　absorption　fine　structure　spectroscopy,　electron　paramagnetic　resonance　spectroscopy,　UV　Raman　spectroscopy,　and　photocatalytic　degradation　of　ethylene.　The　results　revealed　that　the　photocatalytic　activity　of　the　HZSM-5　originated　from　the　isolated　tetrahedrally　coordinated　iron-oxo　species　present　in　the　zeolite　framework.　The　formation　of　such　active　isolated　iron-oxo　species　was　strongly　influenced　by　the　chemical　compositions　(e.g.,　Si/Al　ratio,　and　iron　content)　and　the　preparation　methods　of　zeolite.　This　could　explain　the　difference　in　photoactivity　of　the　different　types　of　HZSM-5　and　FeZSM-5　zeolites.　Possible　mechanisms　of　the　photocatalysis　on　the　zeolites　were　also　discussed.　©　2007　American　Chemical　Society.