The temperature dependency of a 5-mol% MgO-doped periodically poled lithium niobate waveguide was investigated in this paper. We started with the temperature-dependent refractive index equation for the waveguide. Secondly, the temperature dependency of the second harmonic generation effect was experimentally researched under different temperatures and pump powers. The quasi-phase matched wavelengths, efficiency bandwidths and peak efficiencies of the waveguide were measured. The experimental results agreed with theoretical simulations, which are indispensable in the following all-optical sampling studies based on the cascaded second harmonic generation/difference-frequency generation process in the current device. The temperature dependency of a 5-mol% MgO-doped periodically poled lithium niobate waveguide was investigated in this paper. Secondly, the temperature dependency of the second harmonic generation effect was experimentally The quasi-phase matched wavelengths, efficiency bandwidths and peak efficiencies of the waveguide were measured. The experimental results agreed with theoretical simulations, which are indispensable in the following all-optical sampling studies based on the cascaded second harmonic generation / difference-frequency generation process in the current device.