A physically-unclonable-function (PUF) circuit and the control method thereof are provided, and the control method can be applied to the magnetoresistive device. The control method includes providing a first energy to a plurality of magnetic-tunnel junction (MTJ) devices after initializing the MTJ devices to a resistance state, and determining whether the hamming weight of at least one of the MTJ devices which has a predetermined resistance state is within a predetermined range or not.