The article discusses the influence of the oligomeric resin, hydrogenated oligo( cyclopentadiene) (HOCP), on the morphology and properties of its blends with isotactic poly(1-butene) (PB-1). PB-1 and HOCP are found to be partially miscible in the melt state. Solidified PB-1/HOCP blends contain three phases : (1) a crystalline phase formed by PB-1 crystals; (2) an amorphous PB-1-rich phase; and (3) an amorphous HOCP-rich phase. The optical micrographs of the solidified blends show a morphology constituted by microspherulites and domains of the HOCP-rich phase homogeneously distributed in the intraspherulitic region. DSC and DMTA results show two glass transition temperatures (T-g), different from the T-g values of the plain components. The lower T-g is attributed to the PB-1-rich phase, and the higher T-g, to the HOCP-rich phase. The tensile properties were investigated at 25 and 80 degrees C. At 25 degrees C, the PB-1-rich phase is rubbery and the HOCP-rich phase is glassy, so the addition of HOCP to PB-1 arouses a noteworthy hardening of the samples and this brings an increase of the Young＇s modulus, E＇ (although the blend crystallinity lessens), and decreases of stresses at yielding point (sigma(y)) and at rupture (sigma(r)). The 90/10 and 80/20 blends show high values of elongation at rupture (epsilon(r)). At 80 degrees C, the blends show decreases of E＇ and sigma(r) values with the HOCP content. These decreases are attributed to the rubbery state of the phases and reduction of the blend＇s crystallinity. At 80 degrees C, all the blends show a high value of epsilon(r). This phenomenon is attributed to the fine-size domain dispersion of the phases and to sufficient densities of tie molecules and entanglements. Finally, the partial miscibility behavior proposed in this article is compared with the miscibility hypothesis reported elsewhere.