The effects of Mach number on turbulence behaviors are investigated by means of direct numerical simulation of compressible turbulent boundary layers with the free-stream Mach numbers 2, 4 and 6.Some typical turbulent quantities, including the velocity and vorticity fluctuations, intermittency, sweep and ejection events and turbulent kinetic energy budget, are analyzed.The turbulence intensities are significantly decreased with the increasing Math number.The onset of intrinsic intermittency occurs nearer the wall for a higher Mach number.The ejection event is more frequent and the sweep event becomes less frequent.Moreover, the magnitudes of turbulent kinetic energy production, diffusion and transport terms are increased and the solenoidal dissipation is slightly decreased as the Mach number is increased.