A two-dimensional periodically poled lithium niobate crystal with a 13.64 μm period was fabricated. The inverted duty cycle was about 23%. The second harmonic output for the second-order quasi-phase-matching (QPM) against the input was measured. The maximum second harmonic internal conversion efficiency was higher than 40%. All results implied that the second-order QPM could be used to obtain high-frequency conversion efficiency. Compared with the first-order QPM, the second-order QPM can reduce the requirement for the poling technique and the mask fabrication.