Flett Glacier refers to two glaciers on the northwestern flank of Mount Rainier in the U.S. state of Washington. The glaciers lie on a subsidiary peak of Rainier, the Observation Rock. There are two sections of glacial ice, an eastern lobe at about to in elevation, a smaller western lobe at about in elevation. Meltwater from the glacier flows into the Puyallup River.
Flett Glacier commemorates the botanist John B. Flett, who climbed Little Tahoma in 1895.