A statement early on Friday said his half brother, Salman, had become king.
Before the announcement, Saudi television cut to Koranic verses, which often signifies the death of a senior royal.
King Abdullah, who was said to be aged about 90, had been in hospital for several weeks suffering from a lung infection.
Abdullah came to the throne in 2005 but had suffered frequent bouts of ill health in recent years.
(BBC News)