The effect of the electron-phonon interaction on the Optical Kerr effect is investigated theoretically for electrons confined in a core-shell quantum dot.The interactions of electrons with different phonon modes in the core-shell system,including the confined longitudinal optical (LO) and the interface optical (IO) phonon modes,are investigated.It carried a detailed calculation of Optical Kerr effect on a ZnS/CdSe core-shell quantum dot as a function of pump photon energy with different incident photon energy and under different sizes.The results reveal that the polaron effects are quite important especially around the peak value of the third-order susceptibility.