An investigation into a turbulent channel flow subjected to spanwisewall oscillation is carried out via direct numerical simulation. By walloscillation, turbulence is suppressed and friction drag is reduced. Thetransportation of Reynolds stresses under the influence of theoscillating wall is analyzed at the initial and statistically stationarystages to further disclose the mechanism of turbulence suppression anddrag reduction. It is found that the moving wall can cause the transientgrowth of spanwise velocity fluctuations only at the very beginning ofwall oscillation and thereafter the pressure-strain terms play animportant role. The attenuation of turbulence intensities and skinfriction at the statistically stationary stage is mainly due to thesustained reduction of the pressure-strain terms.