About 120 positions will be made redundant from Arnott's Biscuits' Marleston site in Adelaide.

The positions will be moved to the biscuit-maker's production sites in Brisbane and Sydney, which have the capacity to absorb the production cuts.

The company has spent $150 million upgrading its Australian sites in the past five years, which has created two so-called super sites in Sydney and Brisbane.

Investment at Marleston has seen it maintain specialist equipment for more complex products.

Campbell Arnott's Asia Pacific supply chain vice-president Craig Funnell said land restrictions at the Marleston bakery prevented the site from expanding to increase production levels.

However he said the Marleston site will still have a specialist role producing more intricate varieties of biscuits such as Iced Vo Vos and Venetian biscuits.

Mr Funnell said the move helped Arnott's Biscuits remain competitive, with better use of its assets.

"To remain competitive in a global market, we need to embrace improved technology and asset utilisation," he said.

The Adelaide positions will be cut over the next 18 months after consultation with staff and unions.

"Arnott's is committed to supporting our team during these changes. That will include offering outplacement support such as career counselling, resume preparation and interview coaching," Mr Funnell said.

Following these changes, Marleston will continue to produce approximately 7,500 tonnes of biscuits and 8,000 tonnes of liquid chocolate annually.