Abstract: The paper presents the results of an experimental investigation on the unsteadiness of shock-wave/boundary layer interactions generated by ten ramps with streamwise angles of 15, 20 and 24 deg. and sweptback angles of 0, 20, 40 and 60 deg. respectively at Mach numbers of 2.011, 2.504 and 3.015. The results show that: (a) The interactions are cylindrical for all unswept and most of the 20 deg. sweptback interactions and quasi-conical for highly sweptback interactions. The decrease of Mach number or the increase of sweptback angle is favorable for the changeover from cylindrical to quasi-conical interaction. (b) The pressure fluctuations in the intermittent region show sharp low-frequency peak. The peak decreases with increasing sweptback or decreasing streamwise angle. However, with the increase of Mach number, the peaks decrease in cylindrical interactions but slightly increase in quasi-conical interactions. The average shock strength is a governing parameter in quasi-conical interaction.