The demand on high-quality and low-cost healthcare and medical diagnoses/treatment has been rapidly increased as the aging society is coming. Medical electronics becomes an exciting research frontier of future electronics industry where intelligent instrument/clinical devices which treat intractable neurological disorders or chronic diseases, advanced biomimetic devices/systems, artificial organs, etc. are developed with heterogeneous integration of technologies. Medical electronics is an area that bridges engineering, biology, and medicine disciplines and has great opportunities for industry and new science findings. Two implantable medical electronic systems will be presented. One is the sub-retinal implantation system for visual prostheses and the other is the close-loop deep brain stimulation (DBS) system for epilepsy. The sub-retinal implantation system transforms light into electrical pulses to stimulate ganglion cells to restore vision. The DBS system detects patient's ECoG and automatically generates electrical stimulating pulses to suppress epilepsy. Finally, research challenges and perspectives of medical electronics will be discussed.