High speed optical switch is a key device for optical communications system. Many kinds of multimode interference (MMI) waveguide switch have been reported by using thermo-optical polymer whose response time is limited in milisencond orders. In order to obtain a high speed and low energy consumption properties, electro-optic (EO) polymer have been studied for a long time. However, it is diffcult to use EO polymer in MMI because the change of refractive index of EO polymer is small. In this work, we propose an EO polymer MMI waveguide switch with tapered access waveguides. The device consists of the tapered waveguides and multimode waveguide, where the interference condition and the light propagation are controlled by the change of the refractive index of EO polymer. Results of the beam propagation calculation show that the large effect of switching can be achieved by EO polymer having electro-optic coefficient (r33) of 100 pm/V. The cross talk in the device researches at 30 dB for both TE and TM polarizations. The figure-of-merit given by the products of half-voltage (V) and the active length (L) of the electrode was estimated to be VL=0.5Vcm. © 2010 Published by Elsevier B.V.