THE WA Nationals have preferenced the Greens ahead of their Liberal alliance partners on the ticket for two upper house regions in next month's state election.

The Liberal Party's newly-installed agricultural minister Mark Lewis has been listed behind Greens legislative councillor Robin Chapple in the Mining and Pastoral region.

In the South West region, the Nationals have preferenced Greens candidate Diane Evers above Liberals Wade De Campo, Robyn McSweeney, Tony Norment and Heather Reid, but Liberal Steve Thomas has been placed behind the four Nationals candidates.

WA Nationals spokesman Nathan Quigley downplayed the significance of the move, which comes after a preference deal between the Liberals and One Nation emerged.

Mr Quigley said his party had a lot in common with the Shooters and Fishers and also expected the Liberal Democrats and Australian Christians to be competitive.

"Our votes will go towards getting one Liberal elected in each region, which they haven't done for us," he told AAP. "They've got our first candidates below other candidates everywhere else .... and then we go to the Shooters and Fishers after that.

"This is a done thing on both sides now.

"We've done what we can to get our guys up."

The Nationals and the Liberals were coalition partners after the 2008 election and became more distant alliance partners in 2013.

Last year, cracks in the relationship started to show when the Nationals opposed parts of the Liberals privatisation agenda, which aims to reduce the state's ballooning debt.