In the present investigation, flow structures over a slender delta wing with a 70 degrees sweep angle, ? at an angle of attack, alpha of 30 degrees, and under the variation of yaw angles within the range of 0 degrees <=beta <= 20 degrees were investigated experimentally. To analyze the flow structure qualitatively and quantitatively, dye visualizations, surface oil visualizations, surface pressure measurements, and velocity measurements using the stereo particle image velocimetry (PIV) were conducted at Reynolds numbers of Re=2x10(4) and Re=1x10(5). Instantaneous and time-averaged flow data were analyzed to demonstrate the effect of yaw angle (beta) on the alterations of leading-edge vortex formation, vortex breakdown, and also vortical flow structures over the wing surface. Time-averaged distributions of streamwise velocity component, u over bar /U, transverse velocity component v over bar /U, patterns of streamline, psi, and distributions of turbulent kinetic energy TKE/U2 were presented to reveal the physics of flow structures under yaw angle (beta) variations. Distribution of pressure coefficients, (-Cp) at various x/c and y/c locations were also presented. The experimental results demonstrated that the variation of yaw angles (beta) has a strong effect on the alterations of the flow structure, the leading-edge vortex formation, and its breakdown. An increase of yaw angle (beta) causes asymmetrical flow structures and hence expands this asymmetrical flow domain further. (c) 2019 American Society of Civil Engineers.