This study focuses on understanding the difference between conventional and microwave (MW) heating to obtain magnesium and zinc aluminate spinels (MgAl₂O₄ and ZnAl₂O₄) starting from raw oxide powders (magnesia/alpha-alumina, magnesia/gamma-alumina and zincite/alpha-alumina mixtures). The samples were prepared from these different oxide precursors and submitted to different thermal cycles in a MW multimode cavity. The evolution of phase composition was studied by X-Ray Diffraction (XRD) analysis. The choice of the precursors aimed at studying the influence of the difference of dielectric properties and of the specific surface area on the phase formation under MW. It was shown that spinel phases could be obtained by rapid MW thermal cycles (i.e., 100 °C/min under MW vs 25 °C/min under conventional heating). The presence of ZnO as a MW absorbent was beneficial for the MW/material interactions. But, for the three considered mixtures, a SiC susceptor was necessary to facilitate heating