Roll bonding between STS and Mg alloy by inserting aluminum alloy is one of the best ways to produce lightweight 3-ply laminated composite to circumvent the difficulty of direct bonding between STS and Mg alloys. However, Mg/Al interface has a drawback such as poor bonding strength, which has to be overcome to widen the application field of this material as a structural component. In order to enhance the bonding strength of Mg/Al interface, a great number of post roll-bonding treatments have been tried such as annealing or rolling processes. In this study, a series of secondary rolling process has been performed under various process conditions to evaluate the influence of thermo-mechanical treatment on interface microstructure and mechanical properties of STS-AI-Mg clad sheets.