To investigate the dependence of the sensitivity of optical waveguide sensors on the polarization of guided modes, we have analyzed their absorption coefficients for both TE and TM modes by group index method [D.-K. Qing, X-. M. Chen, K. Itoh, M. Murabayashi: J. Lightwave Technol. 14, pp. 1907-1917, 1996]. As field distributions of TE and TM modes are different, the absorption coefficient for TE and TM modes are different. For open clad type evanescent wave sensors, whose mode is more favorable depends on whether the refractive index of the measurand is lower or higher than that of the substrate; for buffered clad type evanescent wave sensors, This depends on the role of the buffer layer; for sensing layer type evanescent wave sensors, TE mode has larger sensitivity than TM mode; for guided wave sensors, both TE and TM mode are suitable for highly sensitive sensors.