Hyper-Rayleigh scattering (HRS) experiments performed on nanometer-scale SiO2/water interfaces (aqueous colloidal suspensions) display finite, measurable signals. HRS is not constrained by the orientational, size, and/or charge restrictions inherent to conventional interfacial second harmonic generation (SHG) or electric-field-induced SHG measurements. Thus, apparently for the first time, the second-order nonlinear optical (NLO) response of ultrasmall interfaces has been measured. pH- and electrolyte-dependent experiments show the response to be sensitive to changes in chemical composition at the silicon dioxide/solution interface. HRS provides detailed information about the surface of these technologically interesting and important particles in their native solution-phase environment.