The laminarization phenomenon of the turbulent boundary layer in an axially rotating pipe was investigated experimentally by introducing an undeveloped flow into it. In the inlet region, the turbulence in the boundary layer was seen to be largely suppressed by the pipe rotation. However, this laminarized boundary layer tended to be unstable as the flow proceeded downstream, and intermittent large-scale bursts of turbulence occurred periodically. Measurements of the Reynolds stress components using conditional sampling techniques revealed that the bursts exert a positive torque around the pipe wall.