Olavi Erämetsä (born Enwald; 10 October 1906 Lahti, Finland - 3 January 1974 Helsinki, Finland) was a Finnish chemist at the Helsinki University of Technology (TKK, now part of Aalto University).  He served as a lecturer in analytical chemistry (1940-1946) before succeeding Yrjö Kauko as professor of inorganic chemistry (1947-1973).
Erämetsä was a major initiator of geochemical research in rare earths and trace elements  at TKK from 1947 to 1973.
In 1965, he reported the isolation of the element promethium from natural sources.
Erämetsä studied the presence of trace elements including rare earths in soils and plants such as lichens and mosses. He also studied their presence in the human body, gathering epidemiological evidence about environmental factors and their possible effects on human health.
Erämetsä was the Chairman of the Finnish Chemistry Society in 1945–1946, a Founding Member of the Finnish Academy of Engineering in 1957 and a Member of the Finnish Academy of Sciences as of 1961.