Grain boundaries (GBs) and their migration play a significant role in the deformation and texture modification of Mg alloys. However, their response to deformation, particularly in terms of their interaction with moving dislocations, is not completely understood. In this study, GB and dislocation properties in Mg and its alloys were first investigated by atomistic simulations employing various semi-empirical potentials. For GB segregation, a strong correlation between the per-site segregation energies of alloying elements and the excess free volumes at GBs was identified. These results were compared with available experimental data and first-principles calculations. Moreover, to describe the role of solute segregation at interfaces, the deformation behavior of Mg and Mg-X (X = Y, Zn) bicrystals with <11-20> symmetric tilt boundaries were studied under plane-strain compression experiments. Characterization by atom probe tomography was used to validate correlative atomistic simulations of the decorated interfaces. The outcomes of this study provide insights into the characteristics of interfacial segregation at GBs in Mg alloys and its impact on plasticity.