Polycondensation of furan derivative by singlet oxygen, which is generated using the sensitizer such as fullerene C-60, is applied to the crosslinking of polymers. A polymer having furan units in the side chains was synthesized by the polymerization of furfrylmethacrylate with 2,2＇-azobis (isobutyronitrile). A 1,1,2,2-tetrachloroethane solution of the polymer was exposed to visible light in the presence of several sensitizers. The solution turned to a gel after several hours and then solidified completely. Photochemical studies and quantum calculations reveal the predominant of fullerene in photocrosslinking of the polymer.