The impact of inlet unstart phenomena on supersonic transport (SST) was investigated by wind tunnel testing. Inlet unstart condition was simulated by controlling the captured mass flow by the inlet. Unsteady pressures on the lower surface of wing and unsteady forces of the wind tunnel model were measured. Unsteady pressure measurement was carried out to detect shock wave motion. Unsteady force measurement by using both internal balance and accelerometers was to estimate axial/angular acceleration of airframe when inlet unstart was occurred.The pressure measurement data revealed that shock location fluctuated with dominant frequency although the controlled mass flow was steady. And it was analytically shown that the dominant frequency is corresponding to the first order frequency of organ pipe resonance. The aerodynamic force measurement data revealed that the angular acceleration in roll direction was found to be dominant and the magnitude of the acceleration seems to be relatively small because of the large size aircraft.Finally, the fluctuation frequency of shock wave and axial/angular accelerations were estimated for the conceptual SJAC's SST.