Riblets are effective approach to improve the aerodynamic performance of low speed wing configurations. For a delta type wing, it is important to alleviate the flow features such as large rollup and tip vortices in low Reynolds number. In this paper, for first time, the effect of the square riblets on delta wings is studied. In the first step, flow visualization is accomplished to find out the effects of riblets on the flow pattern. For this purpose, two slender delta wings with and without riblet are examined in a vertical wind tunnel in which smoke stream lines are passed over the delta wings to visualize the flow pattern. The visualization tests are performed at five angles of attack; i.e., 0, 10, 20, 30 and 35 degrees. The results of flow visualization indicate that considerable improvements are obtained because of delaying flow separation at high attack angles. In the second step, the aerodynamic performance of the two delta wings are quantitatively evaluated by measuring the lift and drag forces using two load cells in another wind tunnel. The force tests are performed at attack angles of 5–65 degrees with 5-degree step sizes. The measured forces show that the riblets decreases the drag coefficient for all attack angles and increase the lift to drag ratio more than 12 percent for 5–20 degrees attack angles.