The microstructure and monomer sequence distribution of polypentadiene-1，3 obta-ined with naphthenate neodymium catalyst have been examined by IR．1H and 13C-NMR spectroscopy．The results show that 1，3-pentadiene enters in polymer chain predomin nantly as cis-1，4 unit (70％ mole) and trans．1，2(25％mole) with minor fraction of trans-1，4 units (5％mole)．Based on our new set of empirical parameters for calculat-ing chemical shifts，the assignment of carbons in the aliphatic region of 13C-NMR spe-ctra has been given．Thus cis-1，4，trans-1，4 and trans-1，2 units-and sequences of monomers can be identified by 13C-NMR spectroscopy．It is found that monomer units of the polypentadiene-1．3 exist only in head-to-tail structure without any head-to-head or tail-to-tail structure．Sequence of 1，4．1，2 has been also observed．In addition．we have measured the spin lattice relaxation times(T1) for carbons of cis-1，4 units．