An ESD (Electrostatic Discharge, ESD) protection circuit includes a voltage-divider generating circuit, a decision circuit, and a switching circuit. The voltage-divider generating circuit outputs a first voltage and a second voltage according to an input voltage. The decision circuit is coupled to the voltage-divider generating circuit and receives the first voltage and the second voltage. The decision circuit outputs an output voltage according to the first voltage and the second voltage. The switching circuit is coupled to the decision circuit and is either turned on or turned off according to the output voltage. The transient voltages of the first and the second voltage are different.