Five years ago, there were fewer than 40 red squirrels on the whole of Anglesey.
The Anglesey project is backed by the European Squirrel Initiative and its spokesman said the work on the island had "nationwide significance".
He said: "It proves that if we can rid our forests of the alien grey squirrel, it is possible for the native reds to re-establish themselves.
"The grey squirrel has now colonised 90% of England and Wales and is widespread in Scotland."
Across Britain, there are about 2.5 million greys and only 60,000 reds.