Hydroboration polymerization of dicyanooligothiophenes bearing various numbers of thiophene repeating units gave the corresponding pi -conjugated poly(eyelodiborazane)s having oligothiophene units, and their light-emitting properties were studied. The polymerization was carried out by adding a THF solution of mesitylborane (or tripylborane) to a suspension of dicyanooligothiophene monomer in THF at room temperature under nitrogen. The reaction mixture was stirred overnight, and the polymer was isolated by reprecipitation as a powder. These polymers were soluble in common organic solvents such as THF and chloroform, and stable under air and water. In UV-vis absorption spectra and fluorescence emission spectra of the polymer solutions, their absorption and emission maxima were bathochromic shifted as the number of thiophene repeating units increased. The light-emitting properties of the poly(cyclodiborazane)s were successfully controlled in this way.