This work is designed to study crack development and resistance changes in aluminum thin films under stretching. Crack development and relative electrical resistance change (Delta R/R(0)) of aluminum thin film on 127-mu m poly ethylene terephthalate substrates were investigated as a function of engineering strain. Four thicknesses were considered for the aluminum thin films: 50, 100, 200, and 500 nm. The engineering stress-engineering strain curves were very similar for all thicknesses. Three strain rates were considered in this study: 0.1 min(-1), 0.5 min(-1) and 1.0 min(-1). Before the yield point, there was no stress difference under different strain rates. However, after the yield point, stress was higher at a higher strain rate. It was found that Delta R/R(0) was very sensitive to the film thickness. Optical microscope images at high magnification showed that cracks were observed at 2% strain for 100, 200, and 500 nm-thick films and at 8% strain for the 50 nm-thick films. Short lateral cracks (perpendicular to the original cracks) were observed at 20% strain for the 100 and 200 nm thick films and at 30% for the 500 nm thick films. Published by Elsevier B.V.