UART (Universal asynchronous receiver/transmitter) is a hardware device that converts data into serial format and tra nsmits it, and is widely used for system diagnosis and debugging in most embedded systems. Hackers can access system memory or firmware by using the functions of UART, and can take over the system by acquiring administrator rights of the system. In this paper, we studied secure UART to protect against hacker attacks through UART. In the proposed sch eme, only authorized users using the promised UART communication protocol are allowed to access UART and unauthoriz ed access is not allowed. In addition, data is encrypted and transmitted to prevent protocol analysis through sniffing. The proposed UART technique was implemented in an embedded Linux system and performance evaluation was performed.