The ex-monarch had been a frequent visitor to China, where he received the bulk of his medical treatment.
One of Asia’s longest-serving monarchs, the former king abruptly quit the throne in October 2004
His had suffered from a series of health problems recently, including cancer, diabetes and hypertension.
Despite abdicating, the ex-monarch sometimes used his website to communicate with the outside world.
In a message in January, he said he wanted to be cremated upon his death and have his ashes kept in an urn inside the Royal Palace, reversing an earlier wish to be buried.
Sihanouk came to the throne in 1941 at the age of 19. He went on to rule Cambodia off and on more than 60 years.
Sihanouk was heralded for bringing his ancient kingdom through independence from France, war and genocide to form a fragile democracy.
He abdicated the throne to his son, Norodom Sihamoni, in 2004 due to health concerns.
Contributor D. Chandler