The book sale will be held at the Scottish Hall on Esk St from May 28 to 30 May.
Rotary Club of Invercargill Charitable Trust book sale chairperson Richard Russell said the cap collection had been gathered from throughout the world.
"We've got thousands of them."
Many had been bought at sporting events including a rugby world cup and still had the price tag on.
"They've never been on anybody’s head."
The book sale was always well-supported and people enjoyed coming.
"The timing of it helps in Invercargill because we're going into winter months and people probably read a lot more books in the winter time when they can't get out and about in the gardens."
Preparations for the event were going well, Mr Russell said.
"There’s plenty of really good quality books this year already that we've got and hopefully that’s attractive to the public that come along to want to buy some.
It was the 45th year the book sale had been held and throughout the years more than $1 million had been returned to community projects.
This year Ngā Kete Matauranga Pounamu Charitable Trust had been chosen as the major recipient of the funds raised.
"This year just happens to be a charitable trust helping a charitable trust which is quite unique too."
The work of Ngā Kete in the community aligned strongly with Rotary’s values of service and impact, Mr Russell said.
"The book sale is truly by the community, for the community."
If people wanted to give books for the sale the staffed service stations throughout the city were drop off points.
Ngā Kete chief executive Tracey Wright-Tawha said the organisation was honoured to be the major recipient.
"This support will help us continue our work and extend our reach to those who need it most."
