Riley is known for her play with colour
Artist Bridget Riley and filmmaker Ken Loach have both won the prestigious Praemium Imperiale art prize.
The Japan Art Association honours five recipients every year for their contribution to international arts and culture, each receiving £85,000 in prize money.
Riley is the first British woman to win the award since it began in 1989 and it is also the first time there have been two British winners in the same year.
"It has come out of the blue and is very delightful in that way. It also means something to the people who have believed in and supported my work in difficult times," said Riley.
Riley has been working for nearly four decades and is one of Britain's most famous contemporary artists, credited with pioneering "Op Art" through her 1960s optical effect paintings.
A retrospective exhibition of her work is currently showing at London's Tate Britain gallery.
Loach also came to prominence in the 1960s with his BBC homelessness documentary Cathy Come Home.
A theme of social injustice runs throughout his films such as Kes, My Name is Joe and his most recent, Sweet Sixteen, which premièred at the Cannes film festival last year.
Loach paid tribute to the people with whom he has worked.
Loach's films often deal with the class system
"Films are a collective effort and I have not made a single film where I've been without a group of friends, writers and actors, and together we have done what we have done," he said.
The three other laureates for 2003 are Italian conductor Claudio Abbado, Italian artist Mario Merz and Dutch designer Rem Koolhaas.
Previous recipients include David Hockney, Frank Gehry, John Gielgud, Ingmar Bergman and Peter Brook.
Loach and Riley will travel to Tokyo later this year to receive their prizes from patron of the Japan Art Association, Prince Hitachi.
They will also meet the Emperor and Empress of Japan.