Anthony Daniels, 77, is parting company with items from his personal collection via Hertfordshire-based auctioneer Propstore from Thursday.
The famous gold helmet he wore for his character in the first film from 1977 is estimated to sell for up to Â£1m.
Daniels said he was excited for his collection to "find a good home".
"I realised I had these items and they're not unloved but they are unlooked at - we don't have them crowding the sitting room," he said, explaining why he has chosen to sell the items now.
"Will I feel sad to part with them? No. I will enjoy the fact people will cherish and display them."
He has put nearly 200 items up for sale at the auction including part of his C-3PO costume, scripts he used during production and even parts of legendary spaceship the Millennium Falcon.
"I did rescue those pieces of the Millennium Falcon from a bonfire at the back of Elstree Studios after production finished on Return of the Jedi," he recalled.
It is estimated those various scraps of Han Solo's beloved ship could sell for a total of Â£9,000.
His hand-annotated dubbing scripts for The Empire Strikes Back could sell for more than Â£1,000.
He said: "Those are so real, it takes me back to standing in front of the dubbing screen."
The actor does still have some Star Wars memorabilia on display in his home.
He has a small Lego brick statue of his character he was given after working on a Star Wars Lego film.
He also has a C-3PO statuette, designed to look like an Oscar, which he kept from production company Lucasfilm.
The Wiltshire-born thespian said he has no plans to auction those, "I'll take those to the grave" he said, firmly.
Daniels revealed while working on the final film of the saga, 2019's Rise of Skywalker, he was told he could take items off the set if he wanted, "but I've got enough," he added.
Propstore will start auctioning various items from film and TV, including the C-3PO head, on Thursday at BAFTA's Piccadilly base in London.
The actor, who will be attending the auction, said he feels "very good about it and very excited" about the event.
The auction will last until Sunday with most items from the Daniels' collection expected to go under the hammer on Saturday.
"Propstore have beautifully and carefully curated the collection.
"In a curious way it means more to them than it does to me, because I have the real memories - I was there," he said.
The actor who played C-3PO in Star Wars said "it feels like it is time" to sell the costumes, props and scripts he kept from the iconic films.