The charity hopes to raise more than £3.5m to pay for drugs which will stop mothers from passing on the HIV virus to their children.
Neeson, who played Jedi Knight Qui-Gon Jinn, persuaded director George Lucas to allow a lightsabre to be sold for the first time.
The Irish actor is selling the fake weapon for charity, spearheading a Unicef initiative aimed at encouraging Hollywood stars to auction film memorabilia to raise money for Movie Action for Children.
The charity hopes to raise more than £3.5m to pay for drugs which will stop mothers from passing on the HIV virus to their children.
Julia Roberts, Mel Gibson and Robert De Niro have also agreed to submit items to the charity auction.
"Needless to say the lithium crystals aren't here so it doesn't switch on," said Neeson, as he held up the lightsabre at a press conference in London on Monday.
"It really is a collector's item - we're expecting to get a lot of money for it," he added.
Julia Roberts will donate the wedding dress from The Runaway Bride, Mel Gibson has agreed to part with the sword used in his epic Braveheart while Robert De Niro will hand over the outfit from US box office hit Meet The Parents.
Schindler's List
Neeson is planning to make a second donation of his own.
He said: "It will probably be my original script from Schindler's List, with coffee rings and, in those days, cigarette ash.
"I was going to give my sword and shield from Rob Roy, but I kind of feel that it pales in comparison to Mel's sword from Braveheart."
Neeson starred as the eponymous hero Oscar Schindler, earning an Oscar nomination for the role.
He added: "My colleagues in the movie industry have reacted in an extraordinary way to the challenge."
Neeson is working with Unicef Ireland - for which he is a special patron - on the auction.
The charity auction will also include items from Sharon Stone and Meryl Streep and will be exhibited in Los Angeles, London and New York prior to the sale.
All the items will also feature in a fund-raising coffee table book.