Veteran actress Shirley MacLaine has penned a manuscript of revelations that could rock Hollywood - but it will remain under lock and key until her death.

The Oscar winner enjoyed a colourful private life, including an open marriage with businessman Steve Parker - during which they both had affairs - and close friendships with Rat Pack stars Frank Sinatra and Dean Martin.

MacLaine has detailed some of her antics in two memoirs, but she's now revealed there are more secrets she has instructed friends to read when she passes away.

"There is a lot I've never told, but that'll be for some of my friends after I'm gone," she told Britain's Guardian Weekend magazine.

Asked if there is an "unpublished manuscript in a safe somewhere", MacLaine replied, "Yep ... Yes ... (I withheld these details) to protect other people. Not myself."