Cyclopolymerization of bis(diazocarbonyl) compounds is described for the first time. By choosing appropriate reaction conditions and monomer structures, the cyclopolymerization of bis(diazoacetate)s efficiently proceeded to give carbon-carbon main chain cyclopolymers with well-defined structures, as confirmed by MALDI-TOF-MS analyses. The products are a new kind of cyclopolymer with respect to polymer structure: there exists no free methylene in the sp(3)-carbon-based polymer backbone in contrast to conventional cyclopolymers prepared from divinyl compounds, which inevitably have free methylenes in and between cyclic units in their polymer backbones. The resulting cyclopolymers with closely aligned cyclic units along the polymer backbone showed a much higher glass transition temperature compared to the corresponding polymers without cyclized repeating units.