Tanera Mor is the largest and only inhabited island in the Summer Isles archipelago 1.5 miles off the north-west coast of Scotland.
The 800-acre island is currently managed by Lizzie and Richard Williams, who took it on from Mrs Williams’ family, the Wilders.
The Wilders bought the island in 1996 after selling their dairy farm in Wiltshire.
Mrs Williams said it is time to give someone else the “privilege of looking after the amazing place”.
Talks with the local community over a buyout were held but it has now been put on the open market.
Mrs Williams said: “After many happy years of calling Tanera home, it is time for someone else to have the privilege of looking after this amazing place.
“We hope that whoever owns the island in the future will enjoy the same warm and co-operative relationship with the community that we have for the past 17 years.”
Estate agents CKD Galbraith described Tanera Mor as a “flourishing tourist enterprise and superb family residence”, with a guide price of STG2.5 million.
It has nine residential properties, a cafe, post office and three jetties.
John Bound, of CKD Galbraith, said: “The chance to own your own Scottish island is extremely rare and with Tanera Mr’s thriving tourist enterprise coupled with being a truly spectacular place to live, we expect to receive a lot of interest as it goes on the open market.
“With on-going support and commitment from the local Coigach community, Tanera Mr offers a truly fantastic prospect for interested parties who will very much have the island’s heritage and sustainability at heart as well as a fantastic life style.”