Polariton dispersion and THz-wave generation in MgO:LiNbO3 single crystal have been investigated by using Raman scattering and THz parametric generation system. The polariton dispersion curve was obtained on the basis of A1(z) mode of Raman scattering experiment. Wavelengths of the idler beam and the THz-wave were calculated using the phase matching condition with the dispersion curve. We have made a TPG system and directly measured the wavelength of the idler beam. The range of the phase matching angle in the TPG system was 0.35~0.80deg, and the frequency of the THz-wave corresponding to the pump and idler beam was measured to be in the range of 0.95~2.30 THz. They agreed well with those calculated by the polariton dispersion curve.