An electronic device and a method for changing modes according to external devices connected through a universal serial bus (USB) and controlling the strength of signals communicated according to changed modes are provided. The method includes detecting a connection with an external device corresponding to booting of the electronic device, determining a mode of the electronic device according to the detected connection with the external device, varying a characteristic setting of an input output (IO) buffer to a certain strength corresponding to the determined mode, and communicating a signal at a strength corresponding to the varied setting.