In this paper, the optimal design of a novel microstrip directional coupler with a grooved housing for high directivity characteristic is presented. It will be shown that the high directivity of the microstrip coupler can be achieved simply by attaching an optimized housing structure. over the microstrip, which is much easier to fabricate than other conventional types. The dimensions of the proposed structure are maximized by using (1+1) evolution strategy (ES) combined with the deterministic algorithm. To improve the effectiveness of the results, efficient optimization procedures suitable for the model are proposed. From these results, it is determined that the proposed structure indicates an improved directivity. The optimized results are verified by full wave analysis at the center frequency of 850MHz.