Abstract: The internal friction (IF) and relative dynamic modulus in the polycrystalline pure aluminum (Al) were measured using a multifunction internal friction apparatus (MFIFA) at frequencies of 0.2,0.3,1.0,2.0 and 3.0 Hz over the wide temperature range between 25 and 450 ℃ with continuous temperature changing.Base on the Arrhenius formula the diffusion activation energy and internal friction behavior features were caculated during increasing and decreasing temperature course.The results show that in the forced vibration of polycrystalline pure aluminum during heating process and cooling process,a distinct IF peak was found in the IF quality factor reciprocal curves.The peak temperature of the IF peak shifted towards higher temperature with increasing frequency,indicating a thermally activated relaxation process.The IF peak was a grain boundary IF peak,which was associated with the diffusive grain boundary of Al/Al.Its activation energy was calculated to be (2.24±0.03)×10-19 J and the pre-exponential factor τ0 was 10-14 s in IF measurements.