The 62-year-old former Black Sabbath singer makes the revelation in an interview published on US website The Daily Beast in the same week that his son, Jack, announced that his fiancée Lisa Stelly is pregnant with their first child.
Asked to name his favourite children's book, the British rocker says: 'Anything with pictures.
'I'm very dyslexic, so I ain't [sic] exactly one to be reading the Harry Potter books to my grandkids.
'They'd be drawing a f****** pension by the time we got to the end of the first chapter.'
Osbourne, who is currently promoting his new book, Trust Me, I'm Dr Ozzy: Advice From Rock's Ultimate Survivor, answers some of his fans' questions on the US website.
Asked how he has managed to stay alive despite years of well-publicised drug abuse, he says: 'In all honesty, I've just been very, very lucky.
'And I'll croak eventually. When? Who knows, man. I don't even wanna know. Although I wouldn't mind knowing where, so I can avoid going there.'
Asked what it is like being married to his wife and manager Sharon, he says: 'A lot f****** easier than it is to be married to me.'