Morphology and rheology of the blends of two commercial polypropylene (PP) grades (designated as MA3 and MM1) with a commercial modifier (EPI) based on hydrogenated oligo (cyclopentadiene) (HOCP) were studied using modulated differential scanning calorimetry (MDSC) and dynamic shear rheometry. Melting and crystallisation points as well as glass-transition temperatures were determined and correlated to blends' compositions. Morphology was additionally studied by hot-stage optical microscopy (HSOM). Molecular characteristics of the materials were determined by gel-permeation chromatography (GPC). Dynamic (oscillatory) shear tests were conducted at different temperatures (190, 210, 230 and 250 degreesC) in a wide frequency range (0.01-300 rad/s) and rheological parameters (such as zero-shear viscosity, activation energy) were also correlated to the composition of the blends. Thermal behaviour of both series of blends suggests phase separation at modifier concentrations above 30%. Dynamic viscosity of MA3/EP1 blends decreased with increasing EP I concentration, while the rheological behaviour of MM1/EP1 system was more complex, due to changing the molecular weight distribution (MWD) of PP component.