In this paper, a polymer electro-optic modulator has been designed and optimized using the full vectorial finite element method. For this purpose, the effects of magnesium oxide (MgO) and down cladding thicknesses, distance between two ground electrodes, hot electrode and modulator widths modulator on the key modulator parameters, such as microwave effective index nm, the characteristic impedance ZC and the microwave losses α are presented. After selecting optimal dimensions of polymer electro-optic modulator, frequency dependent aforementioned parameters and the half-wave voltagelength product (VπL) parameter of polymer electro-optic modulator are extracted and as a consequence, an optimized design is reported. Finally, the optical and electrical modulation responses of polymer electro-optic modulator are calculated. The optimized polymer electrooptic modulator exhibits 3-dB electrical bandwidth of 260 GHz and VπL about 2.8 V·cm in this frequency.