A least-square finite element model was used to model the rheological behavior of both homogeneous and two-phase polymer blends, and their viscosity was calculate over a range of shear rates. The analysis was carried out for a pressure flow situation through a wide rectangular channel. Homogeneous blends were simulated by a model consisting of a large number of alternating layers of A and B components parallel to the flow direction using the adhering layers concept. Heterogeneous blends were simulated by similar alternating layers separated by very thin interlayers. In modeling the negative deviation behavior, associated with the flow characteristics of immiscible blends, the interlayers were assumed to have a viscosity more than one order of magnitude lower than either component. Viscosity values for the interlayers higher than both polymers were used, on the other hand, to represent positive deviation behavior, which is synonymous with the flow behavior of compatibilized blends. To test the accuracy of the model, the computed viscosity results were compared with the values calculated by the more widely quoted equations and also with published experimental data.