The thermal and mechanical fatigue behavior of thin metal films on polymer substrates has been investigated and compared for different combinations of materials, which are typical for micro-optical components: gold or aluminum film deposited on PolyCarbonate (PC) or PolyMethylMethAcrylate (PMMA) substrate. Mechanical fatigue testing has been carried out using an experimental setup, which allows for testing in an equi-biaxial loading condition, mimicking the strain state of the film during thermal cycling. Using scanning electron microscopy, fatigue damage morphologies for the different film/substrate combinations have been found to be quite different for both thermal and mechanical cycling. Furthermore, our results indicate a somewhat lower resistance of the films deposited onto PMMA as compared to PC to both thermal and mechanical fatigue. Under mechanical loading, Au/PC specimens show a longer time to failure as compared to the Al/PC specimens. Crown Copyright (C) 2008 Published by Elsevier B.V. All rights reserved.