Kay Khosrow (Persian: کیخسرو) is a legendary king of Iran of Kayanian dynasty and a character in the Persian epic book, Shahnameh. He was the son of the Iranian prince Siavash who married princess Farangis of Turan while in exile. Before Kay Khosrow was born, his father was murdered in Turan by his maternal grandfather Afrasiab. Kay Khosrow was trained as a child in the desert by Piran, the wise vizier of Afrasiab. His paternal grandfather was Kay Kāvus, the legendary Shah of Iran who chose him as his heir when he returned to Iran with his mother. The name Kay Khosrow derives from Avestan Kauui Haosrauuah, meaning "he who has good fame".
In Avesta, Kay Khosrow has the epithet of "arša airiianąm dax́ iiunąm", meaning "stallion of the Aryan lands". According to Avesta, Kay Khosrow had a son called Āxrūra. Kay Khosrow sacrificed for Anahita in Lake Chichast for winning a chariot race. He killed Afrasiyab in Lake Chichast as revenge for Siavash who had been killed by Aγraēraθa, son of Naru.
In Pahlavi texts, his name is mentioned as Kay Husrōy. According to Šahrestānīhā ī Ērānšahr, he was born in the city of Samarkand, a city founded by his paternal grandfather, Kay Kavus. Kay Khosrow founded the fire of Warahrān (Persian: Bahram) in the city of Samarkand, and reinstalled another fire by the name of Karkōy in the city of Zarang, which was extinguished. According to Menog-i Khrad, Kay Khosrow ruled over Iran for 60 years, and then handed the power to the Kay Luhrasp. Kay Khosrow destroyed an idol temple by the Lake Chichast, and at the resurrection, he will collaborate with Saoshyants.