Two kinds of electrodeposited copper foils (thickness is 8 and 20 mu m) were loaded statically, and the deformation behavior was observed. In-situ X-ray stress measurement was carried out under tensile loading. Fatigue tests were also conducted to observe the effect of the thickness on the fatigue strength. Change in the line broadening with stress cycles was observed to evaluate the fatigue damage. The tensile strength of 8 mu m foil was higher than that of 20 mu m foil. When the foils were loaded within elastic region, the stress measured by the X-ray method agreed with applied stress. When the plastic deformation occurred, difference between the measured stress and the applied stress became large. The difference of 20 mu m foil was larger than that of 8 mu m foil. Fatigue strength of 8 mu m foil was also higher than that of 20 cirri foil. The value of the full width at half maximum, FWHM, increased rapidly at the first cycle, and then the value became nearly constant. Just before fracture, the value increased again. The change in FWHM corresponded to the change in the accumulated ratchet strain.