Abstract: The damping behavior of commercially pure porous aluminum (FA) was investigated.The internal friction (IF) and relative dynamic modulus were measured at frequencies of 0.5,1.0 and 3.0 Hz over the temperature range of 20-400 ℃.The size of macroscopic pore is 1.0 mm and in large proportions up to 69 vol%.The measured IF show that the damping capacity of FA is enhanced in comparison with commercially pure bulk aluminum.Especially,an IF peak is found and corresponding to a rapid drop of relative dynamic modulus (vs temperature) in the FA specimen.The average value for the activation energy of the IF peak is (1.39±0.03) eV.TEM observations show that dislocation substructures exist near the grain boundaries.Accordingly.The intersecting of such substructures with grain boundaries result in the limittion of sliding process during the viscous sliding of the boundary.