Cu/Al multilayers with atomic ratio of Cu:Al=2:1 and bilayer thickness (A) of 20 nm and 5 nm have been prepared by using magnetron sputtering technique. The solid state reaction of these multilayers were investigated by using XRD, TEM and DSC measurements. The Cu and Al layered films grow preferably along <111> direction for A=20 nm multilayers. Solid solution alpha-Cu is formed at low annealing temperature during the initial reaction. With increasing annealing temperature up to 191 degreesC, gamma(2)-Cu9Al4 phase is formed. For as-deposited A=5 nm film, the presence of alpha-Cu at interface during deposition results in a pronounced reduction of temperature for gamma(2)-Cu9Al4 formation. The activation energies of formation of alpha-Cu and gamma(2)-Cu9Al4 in the A=20 nm multilayers were measured to be 0.56+/-0.03 eV and 0.79+/-0.08 eV, respectively, the later agrees with the literature data.