In this study the rheology, morphology, and interfacial interaction of polypropylene (PP)/polybutene-1 (PB-1) blends in different percentages of PB-1 are investigated. The morphology of cryo-fractured surfaces of samples was studied by scanning electron microscopy (SEM). The SEM images showed a droplet-matrix structure in all range of compositions and the size of dispersed phase increased proportionally with PB-1 content. The miscibility of blends at various compositions is evaluated by viscoelastic parameters determined by dynamic oscillation rheometry in the linear viscoelastic region. A distinct Newtonian plateau at low frequencies is observed and the variations of complex viscosity (?*) against angular frequency (?) for all blends are in agreement with Cross model. The complex viscosity of samples at various percentages of PB-1 showed the log-additivity mixing rule behavior in low frequencies and positive-negative deviation behavior (PNDB) at high shear rates. The phenomena such as decrease in the sensitivity of storage modulus to shear rate in the terminal region, the deviation of ColeCole plots from the semi-circular shape, and the tail in relaxation spectrums at high relaxation times are the evidences of two phase heterogenous morphology. The effect of timetemperature on the phase behavior is studied and the interfacial tension between matrix and dispersed phase was evaluated by using emulsion theoretical models. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012