With the increase of component density and decrease of operating voltage, microcontroller has become increasingly sensitive to electromagnetic interference (EMI), a low current or voltage interference coupled into microcontroller via pins could cause operating failure, or even damaged. Most electromagnetic compatibility (EMC) studies of microcontroller did not take the effects of aging into account. However, component aging can degrade the physical parameters of semiconductor and can change the immunity to EMI. This paper analyses the drift of microcontroller immunity to electrical fast transients (EFT) interference after accelerated aging. The measurements that show the variations in the test results for immunity reveal increasing susceptibility after temperature accelerated aging.