A method and a device for detecting object properties using electro-optically modulated surface plasmon resonance (SPR) based on phase detection is disclosed. In the case of a surface plasmon resonance sensing device according to the present invention, the voltage is applied on the sensing device made of an electro-optic material to modulate the surface plasmon resonance condition by varying the wavevector of the incident lightwave. The relation between the phase of output optical wave and the applied voltage is measured, and the solution concentration or the material property is obtained by using the slope of a regression straight line of this relations. The invention can be used in the experimental arrangements of the attenuated-total-reflection (ATR) structure and the optical waveguide structure, and has advantages of high sensitivity, high stability, small bulk, low equipment cost, etc.