We report the simple measurement of surface layer stress of strengthened glasses by means of leakage waveguide method. Effective surface layer stress was introduced by birefringence of the fundamental mode, and corresponding apparatus of measurement was fabricated. For air-cooled tempered, chemically strengthened, and thermally tempered glasses, values of effective surface layer stress have been measured, and the accuracy of measurement has been analysed theoretically. This method can be used for nondestructive raeasurement of surface layer stress.