Carbon microhoneycombs (CMHs), which can be prepared from a resorcinol formaldehyde (RF) hydrogel using ice crystals as a template, are attractive materials for industrial applications such as solid catalysts and adsorbents in flow system reactors. For such applications, pores in a material are important for mass transfer, but the mesopore volumes of CMHs are smaller than that of typical RF-derived carbons because ice crystals compress RF gels during freezing, and mesopores partly collapse. The introduction of mesopores into CMHs requires an additional step such as HCl treatment in the preparation process, and this increases the preparation time. In this work, we developed a convenient method for introducing mesopores into CMHs, in which dextran was added to the initial RF solution. This simple step increased the mesopore volume from 0.015 to 0.191 cm(3)/g. We investigated the porous structure of the sample at each step in the preparation, and found that dextran protected the porous structure of the RF hydrogel from growth of ice crystals, enabling mesopore introduction. A combination of dextran addition and HCl treatment further increased the mesopore volume to 0.753 cm3/g; this cannot be achieved using HCl treatment alone. This may be because the HCl solution can diffuse through the mesopores introduced by dextran addition, and this promotes pore formation. (C) 2016 Elsevier Inc. All rights reserved.