Dayuan is a historical country located in the Ferghana Valley of Central Asia. It is identified primarily through Chinese historical records, specifically the Records of the Grand Historian and the Book of Han.
The region gained prominence in Chinese accounts following the explorations of Zhang Qian around 130 BCE. Subsequent embassies into Central Asia further documented the area's existence and characteristics during this period.
Modern scholarship generally identifies Dayuan with the Ferghana Valley, which was controlled by the Hellenistic city-state of Alexandria Eschate. This entity is often interpreted as a "Greco-Fergana" city-state.