AbstractAn altered free‐volume state (AFVS) model was developed for the zero‐shear viscosity of homogeneous polymer blends. The model involves a single adjustable parameter and is capable of predicting several complex features of the blend viscosity‐composition behavior. These include negative and positive deviations from additivity, maxima, minima, and sigma‐shaped curves. The validity of the model was tested by comparison of the model predictions with experimental data for several homogeneous blend systems. It is shown that the model is valid within a broad molecular weight range and is more accurate than some of the currently accepted models such as the kinetic network model. Besides, it appears that the AFVS model also may be applicable to blends of incompatible polymers under certain con