Koichi Tanaka (born August 3, 1959) is a Japanese scientist who shared the Nobel Prize in Chemistry in 2002 for developing a novel method for mass spectrometric analyses of biological macromolecules with John Bennett Fenn and Kurt Wuthrich.

In 1983, he graduated from Tohoku University with a bachelor's degree in engineering.
His work was filed as a patent application in 1985, and after the patent application was made public reported at the Annual Conference of the Mass Spectrometry Society of Japan held in Kyoto, in May 1987 and became known as soft laser desorption (SLD).
As of 2008, he is the only person without a post-bachelor's degree to have won a Nobel Prize in a scientific field.