Hydroboration polymerization between mesitylborane and 1,9-dicyanoanthracene (DCA) gave the corresponding polycyclodiborazane having anthracene as the repeating unit. The polymer obtained can be expected to be a novel type of an electron-transporting material or polymer catalyst in photochemistry. Polymerization was carried out under nitrogen by adding a tetrahydrofuran (THF) solution of mesitylborane (2 equiv) to a suspension of DCA in THF at room temperature. After the reaction mixture was stirred for 12 h, an insoluble precipitate was filtrated off. The soluble part was purified by reprecipitation into MeOH to give a yellow powder. Gel permeation chromatography (chloroform, PSt) analysis showed that the M-n of the polymer was 4400 (yield 91%). The polymer obtained was highly soluble in common organic solvents such as THF, chloroform, and benzene, despite the presence of an anthracene ring containing repeat unit. The proposed polymer structure was supported by H-1 NMR, B-11-NMR, and IR spectra. An intense green fluorescence emission spectrum was observed at 494 nm. The relatively high stability of the polymer was shown by its resistance to reaction with air or water and from thermogravimetric analysis behavior.