Foamed aluminium (Al) specimens have been prepared by powder metallurgy foaming technique.At room temperature,variations of its internal friction vs porosity,frequency and strain amplitude were measured systematically.The results indicate that internal friction of foamed Al has such characteristics as follows.It increases with increasing porosity and with decreasing pore size.At lower frequencies,it is independent of frequency;it-has a normal amplitude effect.The damping mechanism of foamed Al has been studied.According to the damping mechanism of foamed Al,the experimental results have been explained with some success.