http://www.bbc.co.uk/news/world-asia-16239693His death was announced in an emotional statement read out on national television.
The announcer, wearing black, said he had died on Saturday of physical and mental over-work.
The BBC's Lucy Williamson in Seoul says his death will cause huge shock waves across North Korea.
Kim Jong-il has been the leader of the impoverished communist country since the death of his father Kim Il-sung in 1994.
He suffered a stroke in 2008 and was absent from public view for several months.
His designated successor is believed to be his third son, Kim Jong-woon, who is thought to be in his late 20s.