The oscillatory response of normal shock wave/boundary layer interaction is studied numerically in a rectangular duct. Different shock Mach numbers are achieved by varying the divergence angle of the duct. The average Mach number upstream of the shock system for no-separation (NS), incipient-separation (NS), appreciable-separation (AS), and big-separation are 1.15, 1.25, 1.40, and 1.60 respectively. The wall static pressure variation and the shock train leading edge variations are analyzed for all cases. The no-separation and incipient-separation cases show a very low amplitude, high frequency oscillations whereas a random, irregular, and intermittent oscillations are observed for appreciable-separation and big-separation cases. The dominant frequency of shock oscillation is reduced for AS and BS cases. The intermittency parameter calculated from the wall static pressure data provides the regions of shock oscillation.