Selective oxidation of methane in a micro fixed-bed reactor by using aqueous H2O2 solution as oxidant was studied. Sub-micrometer sized crystals of HZSM-5 and silicalite-1 with Fe contents below 10 ppm were synthesized. Different methods were used to introduce iron to produce Fe/ZSM-5 zeolites with similar but defined Fe contents. Commercial ZSM-5 with trace amount (175 ppm) of Fe impurity showed considerable methane conversion while over the own nearly Fe-free HZSM-5 no conversion could be measured. Fe/ZSM-5 catalysts prepared by different methods starting from the own nearly Fe-free HZSM-5 showed similar methane conversions and catalysts based on Fe(II) as the precursor exhibited a better performance with regard to retarding over oxidation. The productivities of oxygenates were enhanced more than two orders of magnitude while at the same time obtaining high turnover frequencies (TOFs) of 303 h(-1). A methane conversion as high as 23.5% together with oxygenates selectivity of 90.1% was reached. In contrast to Fe/ZSM-5, Fe/silicalite-1, prepared from Fe-free silicalite-1 by activation via the same post-synthetic preparation methods that were also used to prepare Fe/ZSM-5 and having similar Fe contents, never led to an active catalyst.