Takaaki Kajita of Japan and Canada's Arthur McDonald have won the Nobel Physics Prize for work on neutrino oscillations.
The Royal Swedish Academy of Sciences said the two researchers had made key contributions to experiments showing that neutrinos change identities.
"The discovery has changed our understanding of the innermost workings of matter and can prove crucial to our view of the universe," the academy said.
Kajita is director of the Institute for Cosmic Ray Research and professor at the University of Tokyo.
McDonald is a professor emeritus at Queen's University in Kingston, Canada.
McDonald described the publicity surrounding winning the physics prize as "a very daunting experience, needless to say."
He said his eureka moment was when it became clear that his experiment had proven with great accuracy that neutrinos change from one type to another as they travel from the sun to earth.
Asked what other questions about neutrinos remain to be answered, McDonald said that scientists would like to know what the actual mass of the neutrino is.
The winners will split the eight million Swedish kronor (NZ$1.8 million) prize money.
Each winner also gets a diploma and a gold medal at the prize ceremony on December 10.