A circuit for voltage detection and protection comprises a first block, a first voltage detector, a second block and a second voltage detector. The first block receives a first voltage supply. The first voltage detector detects the first voltage supply and generates a first detecting signal when detecting the first voltage supply level is out of the first operating voltage range. The second block receives a second voltage supply. The second voltage detector detects the second voltage supply and generates a second detecting signal when detecting the second voltage supply level is out of the second operating voltage range. The first block performs a protection operation on the circuit when monitoring at least one of the first and second detecting signals.