The blends of polycarbonate and methylmethacrylate-butadiene-styrene copolymer (PC/MBS) were obtained by a twin-screw extruder. The effects of temperature and MBS content on the rheological properties of as-prepared blends were studied. The results show that the processing performance of PC was significantly improved with the addition of MBS. The apparent viscosity of the PC/MBS blends decreases with increase of temperature. When the mass fraction of MBS is below 15%, the apparent viscosity and visco-flow activation energy of PC/MBS blends decrease with increase of MBS content. At the same time, the non-Newtonian index increases. The PC/MBS blends with the best rheological behavior can be obtained when the mass fraction of MBS is 15%. Then the rheological behavior of PC/MBS blends would deteriorate with increase of the mass fraction of MBS.