A physical unclonable function (PUF) circuit and a PUF system including the same are provided. The PUF circuit includes a plurality of PUF cells each configured to generate an output voltage by dividing a power voltage, a reference voltage generator configured to generate a first reference voltage by dividing the power voltage, and a comparing unit configured to sequentially compare the output voltages of the plurality of PUF cells with the first reference voltage to output data values of the plurality of PUF cells.