The effects of inoculation on the damping property of Mg-8Zn-4Al-0.3Mn alloys have been investigated. The results show that the damping property of ZA84 alloys reduces at room temperature after the addition of RE, whereas the damping property at high temperature increases obviously. The damping property of ZA84 alloys at room temperature and high temperature improves respectively after the addition of Al5TiB. It has reached Q-1=0.01 at room temperature with 0.25% Al5TiB. There exists a damping peak in all alloys at high temperature because of the viscous sliding of the grain boundaries and the inteneration of φ (Al2Mg5Zn2) phase at high temperature. It was found that the addition of RE could delay the temperature of damping peak occurs. The main damping mechanisms of ZA84 magnesium alloys with RE and Al5TiB additions are the dislocation damping and interface damping. The higher the movable dislocation density is, the finer the grains are and the more the grain boundaries and phase interfaces are, the better damping property of ZA84 alloys is.