A first order quasi-phase-matched periodically poled micro-structure MgO∶LiNbO 3 for SHG with 4.8～5.2 μm period, 20 mm length, 18 mm width and 1 mm thickness has been successfully fabricated by applying an external field at room temperature. Because the switching field of MgO∶LiNbO 3 is ～5.5 kV/mm, which is approximately one fourth that of the conventional congruent field, periodic poling of thicker MgO∶LiNbO 3 substrates was successfully performed by means of an electric field poling process at room temperature. Using the sample to double the frequency of a diode laser at 980 nm was studied. About 40 mW of CW 490 nm blue light was obtained pumped by 800 mW of the fundamental power, which corresponds to 5% power conversion efficiency. No obvious optical damage has been observed.