The effects of increasing levels of Si on the microstructure and damping capacities of Mg-Al-Si alloys were investigated. The results show that the morphology of the Mg2Si phase is found to be a function of the Si content. The Mg2Si particles with up to 1.3 % of mass fractions of Si have a Chinese-script morphology and dendritic Mg2Si crystals were precipitated predominantly inside the grains of a 2.3 % of mass fractions of Si-containing alloy. The morphology and volume of the Mg2Si phase as well as the distribution of the Mg17Al12 eutectic have a significant effect on the damping capacity of the alloy. With a low strain amplitude, the dislocation density increases with the formation of Mg2Si particles, improving the damping property, while in the high-strain region, dispersed Mg17Al12 precipitates and coarse Mg2Si particles lead to a reduction of the internal friction.