A great deal of research work has been devoted to lowering the sintering temperature of ceramic powders of varied nature, to fulfil a variety of purposes. Both experimentation and theory show that the sintering temperature of alumina can be lowered to 1400°C and below by using small particle sizes and certain additives like TiO 2 and/or MnO. The general idea is that sintering is aided by the development of a liquid phase at this low temperature, due to the presence of the additives. However, there is no phase diagram available to throw light on this matter. For this reason, the present work was aimed at investigating the phase equilibrium relationships in the ternary, non-condensed system Al 2 O 3 -TiO 2 -MnO, in air.Selected compositions in this system were prepared from reagent-grade oxides, uniaxially pressed into 6 mm cylindrical pellets, fired at temperatures between 1000 and 1650°C for 2 to 22 h, water-quenched, and observed by X-ray diffraction and scanning electron microscopy, the composition of some of the phases identified being evaluated by energy-dispersive spectroscopy. These experiments led to the definition of the compatibility triangles and a tentative location of the boundary curves between primary phase fields is presented.