In 2009, 400 staff were made redundant at Anglesey Aluminium, when it closed its smelting operation.
A re-melt business has operated since then, producing around 250,000 tonnes of metal.
The Anglesey Aluminium Metal (AAM) Board says it has made "extensive efforts" to find options to stay in business, but warned employees last week there was a "strong likelihood" it would have to close.
It says a redundancy programme will include helping employees to find new work, and it will work to try to create a legacy for the local community.
A small team will be kept on to continue de-commissioning, and maintain the site until it is sold.
The AAM Board reognise the outstanding work that has been carried out by the employees and management team at Anglesey Aluminium in addition to their commitment to safety and their excellent work ethic.