The polymerization of butadiene catalysed by the TiBr4-i-Bu3A1，TiBr4-Et3A1，and TiBr4-BuLi systems has been studied．In the catalyst system of TiBr4-i-Bu3Al with ben-zene as solvent there are two molar ratios of i-Bu3Al to TiBr4，which exhibit maximum catalytic activity．The geI content，molecular weight and cis-1，4-content of the soluble part of the polymer decrease with increase of the i-Bu3Al／TiBr4 ratio．The atalytic ac-tivity seems to be greater，when the monomer is first mixed with i-Bu3Al than first with TiBr4．The maximum activity appears to move towards greater i-Bu3Al／TiBr4 ratio，when the polymerization temperature is lowered． If heptane is used as solvent．the rate of polymerization is reduced and only one catalyst ratio exhibits maximum activity．The gel content，molecular weight and cis-1，4-content of the soluble part of the polymer oh-tained all seem to be lower． If triethyl aluminium is used instead of triisobutyl alumi-nium．there are also two catalyst ratios exhibiting maximum activity． When the tem-perature of polymerization is lower the catalytic activity of the Et3Al-TiBr4 system seems to be greater than that of the i-Bu3Al-TiBr4 system．The products obtained from both systems appear very alike．They consist of a large amount of gel and the cis-1，4-content of the soluble part of the polymer iS below 70％．Catalysed by a new catalytic syscem-the BuLi-TiBr4 system butadiene can be polymerized to a product containing the cis-1，4-form higher than 90％． Catalytic activity was observed for BuLi／TiBr4 with molar ratios of 1.5—2.5．The cis-4-content of the product becomes smaller，when the catalyst ratio is greater．The valence states of the titanium existing in the above three catalytic sys-tems have been compared．When the metal alkyl to titanium tetrabromide ratio is lower than 2．the trivalent titanium increases with increase of catalyst ratio． When the catalyst ratio is higher than 2

the trivalent titanium decreases with increase of catalyst ratio in the BuLi／TiBr4 system，while in th eI other two systems the trivalent titanium still in-creases till 100％． It is interesting to note that the catalytic activity of the BuLi—TiBr4 system lies just between the range of catalyst ratios Which possess higher content of trivalent titanium．