Mechanical activation-induced B site order-disorder transition was observed in Pb(Mg1/3Nb2/3)O-3-Pb(Mg1/2W1/2)O-3 of complex perovskite structure. The disorder triggered by mechanical activation can be steadily recovered by thermal annealing at elevated temperature, as shown by XRD diffraction results. The degree of ordering calculated from Raman spectra demonstrates similar behaviors as those of XRD, except in the low ordering states, i.e. when the ordering domain size in 0.4PMN-0.6PMW is out of the coherence range of XRD. The above order-disorder transition was explained by the competition between the activation-triggered refinement of ordering domains leading to disordering and the thermal activation, which builds up the ordering domains. (C) 2002 Elsevier Science B.V. All rights reserved.