To clarify the origin of second-harmonic generation (SHG) from electrically polarized SiO2 glasses, we have investigated the influence of the OH concentration and structural defects in the SiO2 glasses and that of the poling conditions on the intensity of SHG. The SHG intensity was increased with increased OH concentration, and the most intense SHG was observed from the solgel-derived SiO2 glasses containing 2500 parts in 106 OH. On the other hand, the intensity of SHG was not clearly related to the specific defects observable by electron spin resonance and vacuum-ultraviolet absorption spectra. With respect to the poling conditions, the intensity of SHG was the largest when the glasses were poled by 3 kV at 200 °C for 4 h, and χ33(2) was evaluated as 0.37 pm/V, which was ∼8% of χ22(2) for LiNbO3.