Nobel chemistry laureate Ryoji Noyori, 63, paid about 15 million yen in additional taxes after failing to declare 32 million yen in the seven years through 2000, Noyori and sources said Tuesday.
Most of the 32 million yen was lecturing fees and prize money the Nagoya University professor received from overseas, the sources said.
"I didn't know how to deal with the overseas portion," Noyori said. "I think I was very careless."
Even before winning last year's Nobel Prize in chemistry, Noyori had received prominent awards, including the Arthur C. Cope Award presented by the American Chemical Society and Saudi Arabia's King Faisal International Prize for Science.
The Nagoya Regional Taxation Bureau is believed to have pointed out Noyori's failure to pay taxes for such prize money and part of the lecture fees he received from overseas, the sources said.
"I didn't think prize money from overseas would be taxed," Noyori said. "There were also cases in which I would receive a check for travel costs and prize money together, and it was unclear how it should be dealt with."
Noyori paid additional taxes for the portion excluding travel costs, according to the sources.
Noyori received the Nobel Prize in December for his work on chirally catalyzed hydrogenation and oxidation reactions -- a field that contributed to the development of important drugs, including antibiotics and anti-inflammatory and heart medicines.