An experimental wind-tunnel investigation was undertaken to determine the effects of Gurney flaps on a 40-deg cropped nonslender delta wing at a chord Reynolds number of 250,000. In the experiment, the height of the Gurney flaps was varied from 0.01C to 0.05C, and the sideslip angle of the model was selected as 0, 5, 10 and 20 deg. In addition, the 0.05C Gurney flap was serrated with different heights of 0.01C to 0.05C separately. In comparison with the baseline clean configuration results, it was found that the model with plate Gurney flaps can indeed increase the lift-to-drag ratio at moderate-to-high lift coefficients for the wing, and the greatest increment was obtained for the 0.01C Gurney flap. The effect of Gurney flap on the increment of lift-to-drag ratio tends to be not significant with the increase of sideslip angle. Moreover, the 0.05C serrated Gurney flap provides the best performance among the serrated Gurney flaps.