The synthesis of poly (alpha-thiophenediyl)benzylidene (PTB) with high molecular weight is described. Number-average degrees of polymerization reached about 74. The characterizations of the polymer was investigated by H-1-NMR, C-13-NMR, IR, and UV-VIS spectra. The polymer with well-defined structure and high molecular weight was obtained by polymerization at low temperature and in polar solvent. This polymer was thermally stable and a thermal decomposition took place at 391 degrees C under nitrogen and at 370 degrees C under air. The glass transformation temperature was 117 degrees C and this PTB was nonfusible.