Interfacial contribution on the rheological behaviors of immiscible polymer blends was analyzed for polystyrene (PS)/polypropylene (PP) and ethylene-propylene-diene rubber (EPDM)/PP blends at steady shear flow. The observed rheological behavior was compared with Park and Lee model. Both shear stress and normal stress difference due to the interfaces were well described by two parameters, κ and λ(1-μ). Especially, the normal stress difference terms which are related to elastic effect of the interfaces were more apparent than shear stress terms. In 30PS/70PP blends, the blend property was mainly determined by pure component's contribution. The interfacial contribution was more dominant at 50PS/50PP blends, which is due to the increased interfacial area. However, for EPDM/PP blends which has very elastic dispersion phase, the relative magnitude of interfacial contribution was small compared with pure component's contribution, even though it is still large compared with other blend systems. The blend properties were mainly determined by pure component's contribution when the original difference in first normal stress difference of pure components was too high. Park and Lee model was also successfully used to estimate the dynamic interfacial tension of PS/PP blend.