The fine precipitates and grain boundary segregation are critical microstructural features at the nano-scale level in Mg alloys. These features influence the properties of Mg-alloys via precipitation strengthening and grain boundary strengthening and can also influence texture, recrystallization and deformation behavior. In this study, Mg-alloys containing different alloying elements, specifically, Nd, Y, Ca and Zn have been investigated to understand the elemental distribution behavior in precipitates and grain boundaries. Qualitative and quantitative characterization of the elemental segregation was conducted via a series of advanced material characterization techniques, including FIB lift-out, HRSTEM, HAADF, fast STEM-EDS and 3D-APT reconstruction. Our initial results indicate that non-rare earth element Ca segregates into nano-precipitates along with rare earth elements Nd and Y, which is believed to contribute the precipitation strengthening. Meantime, the grain boundary segregation of Y, Zn and Ca is observed, which accounts for the texture modification and the formability improvement of Mg-alloys.