An input circuit suitable for an integrated circuit (IC) and a protection circuit in the input circuit are provided. The protection circuit includes a transistor, a voltage selector, an inverter, a resistor and a switch circuit. The transistor is coupled to an input end of the protection circuit. The voltage selector is coupled to the transistor and the input end of the protection circuit, and outputs a lower one of a voltage at the input end of the protection circuit and a ground voltage to the transistor. The inverter is coupled to the transistor. The resistor is coupled between a power supply voltage and the inverter. The switch circuit is coupled to the inverter, a preset voltage and an output end of the protection circuit and is controlled by the inverter to connect the preset voltage to the output end or to switch the output end to a floating state.