The effects of boundary layer thickness upon the flow around a cube mounted on a ground plane, on which a turbulent boundary layer is developing, have been investigated .The height ratio h/δ, which indicates the ratio of cube height h to boundary layer thickness δ, is varied between 0.29 and 2. 86. In particular the measurements in h/δ=0.72 and 2 .86 on the surface pressure distribution and the drag coefficient of the cube, the reattachment length and the Strouhal number were compared in detail with the past experimental data . The following results are obtained.The reattachment distance corresponding to the tail of the separation bubble behind the cube, the minimum pressure and its position on the ground plane corresponding to the roots of the arch type vortex may be estimated by the experimental equation con-elated with h/δ, respectively. Both the drag coefficient CD and the Strouhal number St decrease with decreasing h/δ in the range of h/δ smaller than about 3, and become nearly the constant values of C0 =1.3 and St=0 .11 in the range of h/δ larger than about 3.