The responses of a ramp separation to a boundary layer disturbed by a laser-induced breakdown in Mach 4.5 flow were investigated experimentally. Flat plate-ramp models with three different ramp angles (20 degree, 25 degree, and 30 degree) were tested. A high-speed schlieren imaging technique at 50 kHz frame rate was used to visualize the flow near the corner of the ramp. The laser-induced breakdown was introduced at the upstream of the model leading edge to generate pressure wave and a confined thermal spot that travel to the downstream of the flow. The laminar boundary layer on the flat plate surface was disturbed strongly by the entropy spot. The suppression of the separated flow at a corner of the ramp model was observed in all of the three different ramp angle models when the disturbed boundary layer passed through the ramp corner.