This paper presents the interaction of a highly underexpanded supersonic jet of Mjet = 3.19 with hypersonic cross flow (M∞ = 6). The jet interaction flowfield was studied through wall static pressure measurement, Schlieren, and oil flow visualization. The results clearly demonstrate that flow separation is a strong function of jet pressure ratio (PR). To understand the overall flow physics, numerical simulations were also carried out. The flow features such as primary, secondary, tertiary, and quaternary vortex in separated boundary layer, horseshoe vortices, and its foot print downstream of the injection port were predicted well.