Symphyotrichum hallii (formerly Aster hallii) is a species of flowering plant in the family Asteraceae endemic to western Oregon and Washington states. Commonly known as Hall's aster, it is a perennial, herbaceous plant with a long rhizome that creates colonies of itself. It grows about NaNcm (-2,147,483,648inches) tall, and has white (sometimes pale violet) rays that open July–August.
Most occurrences of the species have been found at elevations of NaNm (-2,147,483,648feet) in open areas in the Puget Sound region and Willamette Valley, with outliers in Columbia Gorge and central Washington. It is conservationally Imperiled (S2) in Washington state.