Thermal polymerizations and photopolymerizations of 7-alkoxycarbonyl-7-cyano-1,4-benzoquinone methides (methoxy (2a), ethoxy (2b), propoxy (2c), isopropoxy (2d), butoxy (2e), and see-butoxy (2f)) were investigated in the solid state. In the thermal polymerization in the solid state, 2a, 2c, 2d, and 2e polymerized to give glassy solids or a mass of crystals, but both 2b and 2f did not polymerize. In the photopolymerization in the solid state, all monomer crystals except for 2a polymerized to give corresponding polymers as needlelike solids. The needlelike polymer obtained by photopolymerization of highly reactive 2c was amorphous by powder X-ray diffraction measurement. Crystal structure of 2c was determined by single-crystal X-ray structure analysis, and the molecular packing in the crystals was discussed.