The thermal relaxation of second order optical nonlinearity in subsurface layer of a poled soda-lime silicate glass was studied.It is shown that the glass annealing below glass transition temperature leads to Shock full relaxation of the nonlinearity.At the same time, the measurements of Teas thermostimulated depolarization current demonstrate that spatial electric charge formed in the course of the glass polarization relaxes above glass transition temperature.This allows concluding that the second order optical nonlinearity in poled glasses is not induced by the spatial electric charge.