The time dependence of resistance under certain magnetic fields in liquid－heliu m temperature regime for single－phase polycrystalline La2/3Ca1/3Mn1-xCuxO-3(x=0.15) have been experimentally studied.It was found that the behavior does not observe the logarithm lawR∝ln t but p resents an exponent－decaying dependence instead.A possible origin for this expo nent－decaying resistance relaxation was discussed in the paper.It was pointed out that the behavior is related to magnetic impurities that are introduced into the system by Cu－doping on Mn sites.