The Radiata Plateau, 300 hectares of Blue Mountains bushland home to a handful of endangered species, has been bought by the NSW government.

The purchase comes after decades of lobbying by local environmentalists for the last remaining undeveloped peninsula-plateau to be protected. The land will now be incorporated into the NSW national park reserve system.

While the government said the sale of the land was commercial in confidence, it was reportedly advertised for $2.8 million earlier this year, having been owned by one family for almost half a century.

Environment Minister Matt Kean said he had received hundreds of letters from the Blue Mountains Conservation Society, which has been lobbying governments to protect the land, near Katoomba, for 35 years.