Chromium carbonyl complexes were incorporated into a molecularly ordered mesoporous phenylene-silica by reaction with Cr(CO)6 in refluxing 1,2-dichloroethane (DCE). The modified material with a chromium loading of 0.07mmolg−1 was characterised by powder X-ray diffraction, N2 adsorption, thermogravimetric analysis (TGA), FT-IR, 13C and 29Si MAS NMR spectroscopies. TGA under air indicated that thermal decarbonylation between 250 and 350°C preceded the Cr-promoted decomposition and release of organic fragments at a lower temperature (onset ca. 380°C) than that registered for the phenylene-silica precursor (onset ca. 550°C). The catalytic performance of the modified phenylene-silica was evaluated in the oxidation of cis-cyclooctene at 55°C with tert-butylhydroperoxide (TBHP) as the oxidant and DCE as the co-solvent. The main product was the epoxide, formed in 83% yield after 24h, with 2-cycloocten-1-one being the main by-product. Although the activity of the catalyst decreased after the first recycle, possibly due to partial chromium leaching, it remained nearly the same thereafter, and leaching tests indicated that the catalytic reaction was essentially heterogeneous in nature. Tests carried out using a radical scavenger indicated that the reaction of the olefin with TBHP may involve both free radical and non-radical reaction mechanisms.