The electron spin dynamics is investigated by the time-resolved Kerr rotation technique in a pair of special GaAs/AlGaAs asymmetric quantum well samples grown on (111)-oriented substrates,whose structures are the same except for their opposite directions of potential asymmetry.A large difference of spin lifetimes between the two samples is observed at low temperature.This difference is interpreted in terms of a cancellation effect between the Dresselhaus spin-splitting term in the conduction band and another term induced by interface inversion asymmetry.The deviation decreases with the increasing temperature,and almost disappears when T ＞ 100 K because the cubic Dresselhaus term becomes more important.