Chromium-based metal-organic framework (MOF), MIL-101(Cr), has emerged as a potential hydrogen storage material because of its high specific surface area, tuneable pore size, and unique structure. A large portion of voids generated in MOFs remain unutilized for hydrogen storage owing to weak interactions between the walls of MOFs and H2 molecules. The present study was aimed to reduce the unutilized voids in MIL-101 by incorporating microporous activated carbon (AC) into MIL-101 pores and thereby enhancing its volumetric hydrogen storage capacity. MIL-101 and its AC composites were synthesized under hydrothermal conditions by adding AC in different proportions in situ during the synthesis of MIL-101. The synthesized materials were characterized by various physico-chemical methods such as powder X-ray diffraction, thermogravimetric analysis (TGA), N2-adsorption/desorption isotherms measured at 77.4K, and transmission electron microscopy (TEM). AC@MIL-101/A prepared by the incorporation of 0.63wt% of AC into MIL-101 shows the highest hydrogen uptake of 10.1wt% at 77.4K and up to 6000kPa hydrogen pressure. Copyright (c) 2011 John Wiley & Sons, Ltd.