3,4/cis-1,4-Polyisoprenes were prepared with Fe(acac)3-Al(i-Bu)3catalyst. These polymers are of interest because of their higher 3,4 content and different degree of crystallinity. The13C-NMR spectra of these polymers were much more complex than those previously reported and were assigned using slightly modified empirical parameters based on Gronski et al. In order to further clarify the assignments, hydrogenation of the polymers was carried out, and the13C-NMR spectra of the hydrogenated polymers were partially assigned. Based on these assignments, it was found that the existence of long sequences of vinyl monomer units might be a favorable factor for the formation of partially crystallized polymer. Finally, the13C-spin relaxation timesT1, as well as their temperature dependence, were also measured in chloroform-d1solvent at 50 MHz, and the Arrhenius activation energy was estimated.