For over five decades considerable attention has been given to magnesium-based alloys, primarily from the physical metallurgy point of view. The driving force for this effort has been the potential applications of Mg alloys in light weight structural components, namely in the automotive and aircraft industries. However, the processing of these alloys through conventional casting technologies have not succeed in reaching a high level of formability and ductility while preserving high specific strength. The combination of rapid solidification and consolidation techniques has arisen as a promising approach to overcome these limitations[l,2]. On the other hand, rapid solidification technologies are opening a wide field for fundamental studies, since different sets of thermodynamic (stability), kinetic and structural conditions are established to control a variety of solid-state phase transformations. The present work reports the applications of electron microscopy techniques to the characterization of the precipitation behavior in the rapidly solidified Mg-based alloys we are investigating.