An integrated circuit and a transmission circuit thereof are provided. The transmission circuit includes an input buffer and a voltage holding circuit. The voltage holding circuit has a first end coupled to the input end of the input buffer, and a second end coupled to a reference voltage end. The voltage holding circuit includes a switch and a diode apparatus coupled in series between the first end and the second end of the voltage holding circuit. The switch is configured to receive a mode signal, and is turned on or cut off according to the mode signal.