Over-voltage indicator and related circuit and method. The over-voltage indicator can work with an I/O circuit of a chip for detecting over-voltage in an I/O pad and providing an indication signal accordingly. When over-voltage does not happen, the over-voltage indicator continues to detect a signal level of the I/O pad and keeps the indication signal low. Once over-voltage is detected, the over-voltage indicator pauses detecting, asserts a high level in the indication signal, and periodically resumes detecting until end of over-voltage is detected. With informing provided by the indication signal, a core cell of the chip can perform proper operation to reduce potential damage caused by over-voltage.