Abstract: The micro-structures of the fractions and the gel of Ni-catalysed polybutadiene were studied by FTIR. It was shown that the lower motecular weight fraction has higher trans-1,4and vinyl-1,2 contents and the that with higher molecular weight has higher cis-1, 4content, indicating that more trans-1,4 or vinyl units are formed at the earlier period of the chain propagation. The trans-1,4 and vinyl-1,2 contents in the gel are more than those in the sol of the same sampla. It is deduced that there is more structural similarity between the gel and the lower molecular weight fractions.