We present a theoretical study on the dispersion relation for surface plasmons at a metal–Kerr medium interface where the metal is described by a nonlocal dielectric function according to the hydrodynamic model. The Kerr effect leads to a shift of the surface plasmon frequency depending on the electric field intensity, the magnitude as well as the sign of the Kerr coefficient, and the wavevector. We further observe that this frequency shift is largely quenched
for large wavenumbers for which the nonlocal effect is significantly manifested. We account for this quenching quantitatively by a calculation showing how the nonlocality weakens the sensitivity in the metal’s response to the variation of the dielectric function of the Kerr medium. A possible experimental observation of this new effect is briefly discussed.