Blending of hydroxyl-terminated liquid butadiene rubber (HT-BR) with 1-chlorobutadiene-butadiene rubber (CB-BR) was carried out in the presence of isopropylidenedicyclohexyl diisocianate (IPCI) or sulfur as a curing agent. It was found that the HT-BR/CB-BR blend displayed a good plasticity, i.e., its Mooney viscosity became lower than that of CB-BR, which brought about a good processability. The HT-BR fraction (E(S)) from the HT-BR/CB-BR blend vulcanizates, which was prepared by the IPCI-cured system, was evaluated to be ca. 20% by the equilibrium swelling test in benzene. The E(S) of the sulfur-cured blend was ca. 70%. This result shows that HT-BR acted as a reactive softener when it was compounded with CB-BR by curing with the diisocyanate. The tensile strength of the IPCI vulcanizate was exceedingly higher than that of sulfur-cured vulcanizate at all blend ratios of HT-BR to CB-BR.