Colloidal silica templated mesoporous carbons, which not only have a systematically expanded large cage size (5-45 nm) but also controlled window size (5-25 nm), are successfully obtained via spontaneous phase separation of boron species from mixture of carbon precursor, boric acid, and colloidal silica during carbonization process. This novel synthesis offers a new chance to control the pore structure in materials obtained by nanoreplication using rigid templates.