We analyzed orientational relaxation modes in cholesteric liquid crystals using dynamic light scattering(DLS) and electro-optic(EO) response measurements. Assuming that the helical pitch is constant in the deformation process, we theoretically predicted the dispersion relation of two orthogonal relaxation modes in which the director slightly deforms from equilibrium state, and compared the modes with experimental results. Dispersion relation measured in the DLS completely satisfies our theoretical prediction, and extrapolated relaxation frequency (q→0) also coincides with that obtained by the EO measurement. Furthermore, it was found that the helical pitch dependence was well-explained by our theoretical model.