In this paper, the aging characteristics of isotropically conductive adhesive (ICA) joints using surface mount device (SMD)-on-flex technology were investigated, by noting the glass transition temperature (Tg) of ICA. Resistor-on-flex assemblies using ICA cured at 150 degreesC for 10 minutes were subjected to thermal aging at 40 and 125 degreesC for up to 1000 hours. Shear tests and microstructural examination were carried out. It was found that the aged ICA joints had their maximum shear stresses increased during the early stage, indicating the behaviour of further curing in the ICA. The joints aged at the elevated temperature seemed to degrade significantly after 200 hours. When the aging temperature was slightly above the Tg of ICA, significant decrease in shear strength was obtained. Moreover, microstructural examination with scanning electronic microscopy revealed that the significant decrease in shear strength was mainly due to formation of microcracks and delaminations which were caused by thermal mismatches. The fracture surface of the ICA was found to have different morphologies with different aging temperatures.