Their age challenges the accepted view that rice cultivation originated in China about 12,000 years ago.
The rice is genetically different from the modern food crop, which will allow researchers to trace its evolution.
Today's rice is the primary food for over half the world's population, with 576,280,000 tonnes produced in 2002.
Rice is especially important in Asia, where it is responsible for almost a third of all calorific intake.
Tracer of evolution
The oldest known rice was discovered by Lee Yung-jo and Woo Jong-yoon of Chungbuk National University in South Korea.
Radioactive dating of the 59 grains of carbonised rice has pushed back the date for the earliest known cultivation of the plant.
DNA analysis shows the early rice sample to be different from the modern intensively farmed varieties, thereby offering scientists the opportunity to study the evolution of one of the world's principal food sources.
The region in central Korea where the grains were found is one of the most important sites for understanding the development of Stone Age man in Asia.