Abstract: Laboratory experiments have been conducted to study high Reynolds number (from 1×10⁵ to 1×10⁶), three-dimensional lid-driven cavity flows in two cavity dimensions: 0.2m×0.2m×0.2m and 0.5m×0.5m×0.5m. Particle Image Velocimetry (PIV) technical was applied to investigate the flow field and the effects of wall on the flow fields. Measured time-averaged streamlines show that the primary eddy starts to distort at Re=5×10⁵ and starts to breakup into two/three eddies at Re=1×10⁶. The region of Downstream Secondary Eddy (DSE) decreases as the Reynolds number increases. At Re=5×10⁵, a fully developed DSE can be seen clearly. But it is hard to see when Re=1×10⁶. The thickness of boundary layer becomes thinner and thinner as the Reynolds number increases. The measurements also show that the side boundary has a significant impact of the primary eddy.