Quail entrained to 24 h light dark‐cycle exhibited a daily rhythm in the electroretinogram (ERG). The amplitude of the b‐wave was large during day and small during night. Strong light intensity (more than 10 joule) was required to detect this rhythmicity. After opticnervesection the diurnal rhythm of ERG persisted at least 2 weeks in LD 14:10. A 30‐min dark treatment produced a more pronounced difference between day and night level of the b‐wave amplitude. These characteristics of the ERG remained unchanged after exposure to constant dim light condition both in intact and optic‐nerve sectioned birds. These observations suggest that the retinal system itself may be classified as one of the self‐sustained oscillators and be likely to control the daily rhythm of the retinal response to light. The possible role of the retinal system in the photoperiodic response in quail is discussed.