Ruth Armer (1896-1977) was a painter active in San Francisco, California.
Armer studied at the Mark Hopkins Institute of Art (San Francisco Art Institute) and in New York City with Robert Henri, George Bellows, and John Sloan. During her career she worked as a commercial illustrator as well as a landscape and portrait artist. In the late-1930s she experimented with abstraction, a tendency reinforced by contact with the California School of Fine Arts abstract expressionist movement in the late-1940s.
Armer taught for years in the Bay area and was an active exhibiting artist until her death.