Abstract: The effect of polymeric additives PAM on the time-correlation structure of turbulence in the cenerline region of a rectangular pipe was investigated experimentally with a 2-dimensional laser Doppler velocimeter.It was found under the condition of drag reduction that the time-correlation charactenristics of turbulent fluctuating velocities showed obvious changes.At the same Rynolds number,all the time scales of longitudinal autocorrelation,transversal autocorrelation and cross-correlation increased with the additive concentration. This trend of change is consistent with that of drag reduction ratio.A new phenomenon,the time-effect of cross-correlation coefficient at the centreline,is reported for the first time．These results provide further theoretical investigation with new experimental facts,and support the role of viscoelasticity in the mechanism of drag reduction.