This contribution discusses the influence of hydrogenated oligocyclopentadiene (HOCP) on the morphology, the phase structure and the thermal properties of its blends with isotactic poly(1-butene) (PB-1) as a function of composition and crystallization conditions. PB-1 and HOCP are partially miscible in the melt state. The blends, in the solid state, form generally a three-phase system: a crystalline phase formed by the polyolefin and two amorphous phases, of which one is rich in PB-1 and the other one in HOCP. The optical micrographs of the solidified blends show a morphology constituted by microspherulites and domains of HOCP-rich phase homogeneously distributed in intraspherulitic regions. Moreover, when the PB-1 and the blends are isothermally crystallized, hedrite-like crystallites are observed. The crystallization process and the melting behavior are strongly influenced by the presence of the oligomer, since the addition of HOCP decreases the overall crystallization rate and the melting point of the blends.