We demonstrate quasiphase matched second harmonic generation by use of annealed proton-exchanged 87° Z-cut MgO 5 mol &percent; dopedLiNbO3(MgO:LN) waveguides supporting a TE-mode guided wave. Formation of a domain inversion was achieved by applying electric fields in 3° Y-cut and 87° Z-cut MgO:LN. In 3° Y-cut and 87° Z-cut MgO:LN substrates, a polarization axis inclines at an angle &thgr; equal to 3° to the surface. The domain inversion was formed in a direction parallel to the polarization axis like needles stuck into the substrate. The depth of the domain inversion was 2.5 &mgr;m with a period of 4.75 &mgr;m. The depth was about 2.5 times deeper than that in X- and Y-cut substrate at an angle &thgr; equal to 0°. By forming a waveguide on the domain-inverted substrate, a blue light of wavelength 475 nm, and a power of 37 mW has been obtained and a normalized second harmonic conversion efficiency was300&percent;/W cm2with interaction length of 10 mm, using a tunable external cavity laser diode as a fundamental wave source. ©1997 American Institute of Physics.