The formation of perovskite Pb(Mg1/3Nb2/3)O-3 (PMN) by the molten salt synthesis method using sulphate flux has been investigated as a function of calcination temperature and mole ratio between Li2SO4 and Na2SO4. A 97% perovskite phase was synthesized at 750 degrees C for 30 min with 0.635Li(2)SO(4)-0.365Na(2)SO(4) flux without any sub-products affecting the formation reaction of the PMN phase. The percentage of the perovskite phase was influenced by changes in the Li2SO4/Na2SO4 mole ratio at a given temperature. The pyrochlore phase present was identified as Pb3Nb4O13 (P3N2) when 0.635Li(2)SO(4)-0.365Na(2)SO(4) flux was used. The results for other lead-based ferroelectrics are also discussed.