Lee, Yuan Tseh (1936-) was an American scientist who shared the Nobel Prize in chemistry in 1986 for his development of the crossed molecular beam technique for studying chemical reactions.

Yuan Tseh Lee was born in Hsinchu, China, on Nov. 29, 1936. His father was Tse Fan Lee, an accomplished artist, and his mother was Pei Tsai Lee, a schoolteacher. Lee's education began under the Japanese occupation, and then was disrupted by World War II (1939–1945). Nevertheless, Lee completed elementary and secondary school, enjoying sports and music. Lee also read many books.

Due to his outstanding academic record, the National Taiwan University admitted Lee in 1955 without his taking the entrance examination. He chose chemistry as his field. After graduating in 1959, Lee went on to the National Tsinghua University for graduate work. He received his master's degree on the studies of the natural radioisotopes contained in hokutolite, a mineral in hot spring sediment. Lee stayed on at the university as a research assistant and carried out the X-ray crystallography to determine the molecular structure of a type of samarium.

In 1962, Lee moved to the United States to attend the University of California at Berkeley, where he studied chemistry. Upon receiving his Ph.D. degree in 1965, Lee began to work on ion beams. An ion js an atom that is charged because it has gained or lost electrons. Ions can be accelerated by electric fields to form high-speed beams of particles.

In 1967, Lee joined Dudley Robert Herschbach at Harvard University. He successfully developed a universal crossed molecular beams apparatus that enabled scientists to analyze the dynamics of chemical reactions. This technique involved creating high-speed jets of molecules or atoms that collided and caused some individual molecules or atoms to react with each other. From these reactions, scientists could gather information about the behavior of molecules or atoms.

Lee became an assistant professor at the University of Chicago in 1968. There he constructed a more advanced version of crossed molecular beams apparatus, allowing him to perform many pioneering experiments with his students. He was promoted to associate professor in 1971 and professor in 1973. In 1974, Lee returned to Berkeley as professor of chemistry and principal investigator at the Lawrence Berkeley Laboratory of the University of California. He became an American citizen the same year. Lee helped make the laboratory a world leader in research. It contained seven sophisticated molecular beams apparatus that were specially designed to pursue problems associated with reaction dynamics, photochemical processes, and molecular spectroscopy. The laboratory attracted top scientists from around the world.

In 1986, Lee shared the Nobel Prize in chemistry with Herschbach and John Charles Polanyi. Lee earned the prize for developing the crossed molecular beam technique.

In 1994, Lee took the position of President of the Academia Sinica in Taipei, China, a prominent academic institution. He also became distinguished research fellow, Institute of Atomic and Molecular Sciences, at the Academia Sinica.

Lee and his wife, Bernice Wu Lee, met in elementary school and have two sons and a daughter.