Abstract: With the catalyst system, FeCl₃-(i-C₄H₉)₃Al-phen, (cis-1, 4—1, 2)equibinary polybu-tadiene was obtained at the polymerization temperature of-30—50℃. By gas-chromato-graphic analysis of the ozonolysis product of the polymer and ¹³C-NMR determination it was found that the sequence distribution was not of alternating type. The sequence distribution of the polymer at high polymerization temperature appeared near the Ber-noullian statistical and at low temperature it deviated from the random distribution model,The polymerization mechanism has been discussed briefly.