The microstructural evolution during thermal annealing of a cryogenic rolled 5052 Al alloy was investigated. The activation energy for annealing behavior was calculated using DSC data. For the heating rate of 16°C/min, the precipitation occurred at the annealing temperature of 150~230°C due to Mg self diffusion, recovery occurred at the annealing temperature of 230~260°C, and recrystallization proceeded at a higher temperature up to about 370°C. Both recovery and recrystallization gave rise to non-uniform, bimodal grain-size distributions, which may result from heterogeneous nanostructures. In addition, the activation energy for the precipitation was found as ~115kJ/mol, indicating the process was diffusion-controlled (Mg in Al), and the activation energy for recovery was found to be ~140kJ/mol, representing self-diffusion in pure Al.