Koshiba won the Nobel Prize in Physics in 2002, jointly with Raymond Davis Jr., "for pioneering contributions to astrophysics, in particular for the detection of cosmic neutrinos".

(The other shares of that year's Prize were awarded to Raymond Davis Jr. and Riccardo Giacconi of the U.S.A.)[4] Koshiba's initial research was in cosmic rays.

In 1969, he shifted into electron-positron collider physics, and was involved with the JADE detector in Germany, which helped confirm the Standard Model.

Along with Masayuki Nakahata and Atsuto Suzuki, Koshiba designed the Kamiokande experiment to detect proton decay, a prediction of grand unified theories.

[7][1] The deficit would be eventually explained by "neutrino oscillations", whose existence was confirmed by an enlarged version of Kamiokande, known as Super-Kamiokande, run under the direction of Koshiba's student Takaaki Kajita.

[5] In 1987, the Kamiokande experimental detector detected neutrinos from the supernova explosion (designated SN 1987A) outside the Milky Way, the Large Magellanic Cloud.

[9] Koshiba was a member of the Board of Sponsors of the Bulletin of the Atomic Scientists, and also a foreign fellow of Bangladesh Academy of Sciences.