QantasLink will offer direct flights to Kangaroo Island from Adelaide and Melbourne from December in a boost for the island's tourism industry.

The airline will offer five flights a week from Adelaide over the peak summer months, reducing to three flights a week after Easter.

There will be two flights a week from Melbourne but only during the height of tourist season from December 17 to January 28.

The South Australian Government will support the new flights in a joint tourism marketing arrangement between Qantas and the SA Tourism Commission.

SA Premier Jay Weatherill said the island was often the number one Australian icon on recognition lists for Chinese tourists.

"This will allow the fantastic Qantas network to be able to promote Kangaroo Island directly and also to do that with their international partners though the One World network," he said.

"This is very much the arrowhead for South Australian tourism. Come to Kangaroo Island and then explore the other things."

An $18-million upgrade of the Kingscote Airport is due to be completed in November.

Qantas to offer 20,000 seats a year

QantasLink will offer 20,000 seats a year on its new Kangaroo Island routes, using a 50-seat Dash 8 Q300 and 74-seat Q400 aircraft.

It ceased flying to the island 12 years ago but QantasLink chief executive officer John Gissling was confident the latest service would remain.

"The investments in infrastructure, accommodation and all things going on in Kangaroo Island gives us enormous confidence," he said.

"This is about co-marketing a jewel on the Australian map using our enormous networks, our One World partners and our key partnerships such as Emirates and our Chinese operators to really get Kangaroo Island on the map."

The SA Government said the island received 138,000 overnight visitors in the past year, with about half from SA, 22 per cent from interstate, and 29 per cent from overseas.

The airline will compete with existing air services offered by Regional Express (Rex) and the SeaLink ferry service.

SA Tourism Minister Leon Bignell said the service was not "about cutting someone's piece of the pie".

"This is about growing the pie and making sure we get more people from right around the world to this wonderful island."