Abstract: A system and method for detecting a flicker frequency, and electronic device including the system are provided. The system includes an optical sensor, a sequence generator, a first and a second computing circuit. The optical sensor converts an incident light into a digital sequence according to a sampling frequency, which is greater than at least twice the flicker frequency. The sequence generator generates a first reference sequence and a second reference sequence that is delayed by a period from the first reference sequence, which are periodic according to the flicker frequency and the sampling frequency. The first computing circuit computes a first and a second correlation coefficient. The second computing circuit computes a detection score that indicates a probability of existence of the flicker frequency according to the first and the second correlation coefficient.