A new technique for measuring the electro-optic coefficient of nonlinear optical polymer is described. In anattenuated-total-reflection experiment the refractive index of the poled polymer is changed because of thePockels effect. This change causes a shift of the angular position of the surface plasmon modes that correspondsto a change in reflectivity at a fixed angle. By measuring the change of the light reflectivity at theproperly chosen angle one can calculate the electro-optic coefficient of the poled polymer. Compared withother, conventional methods, here the electro-optic coefficients are given in a simpler form and the requiredparameters are easier to measure. The commonly used lock-in amplifier is not required. This technique is ahighly sensitive method for measuring the electro-optic coefficient because of the newly chosen working interiorangle for which a tiny change in the refractive index leads to a large change in reflectivity.