Magnesium and magnesium alloys have paid an attention on the automobile industry, because of their specific strength and vibration damping capacity. However, the damping capacity of AZ-series magnesium alloy does not have excellent vibration damping capacity, unlike the pure magnesium. Despite the low damping capacity of AZ-series magnesium alloys, studies of AZ- series magnesium alloys have focused on texture control and microstructure refinement, in order to improve room temperature formability. In this study, in order to clarify the influence of aluminum concentration on the damping capacity mechanisms, AZ-series magnesium alloys with different chemical composition(Pure Mg, AZ31, AZ61) were investigated by analyzing the microstructure and internal friction. Three kinds of ingots with different aluminum concentration were rolled at 673K with a rolling reduction of 30%, respectively. Damping capacity test specimens were machined out from rolled plate with parallel to the normal plane. These specimens were annealed at 623K-723K for 30-180 minutes. Then, microstructure was examined by using optical microscopy, and damping capacity was measured by using internal friction measurement machine. As a result in this study, at the beginning of heat treatment, twin structure was disappeared, and static recrystallization of equiaxed grain was occurred. As the heat treatment time and temperature increase, static recrystallization of equiaxed grains was developed, damping capacity was increased with increasing grain size. The C1 value and C2 value of Granato-Lucke equation in damping capacity were varied depending on grain size and solute concentration. With an increase of heat treatment time, C1 value was increased with increasing grain size. Also, with an increase of solute concentration, C2 value was decreased with increasing solute content. Therefore, it is concluded that damping capacity influenced by grain size and solute content.