A perovskite-like phase of lanthanum magnesium niobate, La(Mg_2/3Nb_1/3)O₃ (LMN) has been synthesised by a mixed oxide synthetic route. Both magnesium oxide and magnesium carbonate hydroxide pentahydrate have been investigated as magnesium precursors, with the formation of the LMN phase investigated as a function of calcination temperature and dwell time by DTA and XRD. Morever, particle size distribution, morphology, phase composition and crystal structure have been determined via laser diffraction, SEM and TEM/EDX, respectively. A combination of X-ray and electron diffraction studies has demonstrated that heterogeneous powders are produced, with the presence of an MgO-rich phase and varying Mg/Nb ratios within the parent phase of LMN. Minor phases have also been identified as LaNbO₄, La₃NbO₇, MgO, Mg₄Nb₂O₉ and La₂O₃, with their concentrations decreasing with rising calcination temperature. X-ray and electron diffraction data are supportive of monoclinic symmetry in the parent LMN phase.