SA Best is proposing to cut 18 state MPs in order to make "a bloated and slack Parliament" more efficient, Senator Nick Xenophon has said.

For its first election pledge, the party has announced it wants to reduce the number of Lower House MPs from 47 to 34, and the number of Upper House MPs from 22 to 17.

Members of the Legislative Council would also have their eight-year terms cut in half.

Senator Xenophon said the cuts would save the state $24 million over four years and that money would be better spent on community services.

"Many South Australians wouldn't have any idea who their local state MP is," he said.

"We need this reform because it's a bloated and slack Parliament.

"Making the Parliament smaller will put every MP who'll be elected at the next election on notice to work as hard as they possibly can otherwise they'll end up out of office."

The changes would increase the number of voters for each Lower House seat by about 10,000, meaning South Australia would be equivalent to states including Queensland, which has about 35,000 voters per seat.

Opposition slams proposal

The State Opposition said it would not support the plan as it would have a particularly damaging impact on rural electorates.

"South Australia exists beyond Gepps Cross ... I'm currently in regional South Australia, it's a very important part of our state and we won't be slashing their representation in the Parliament," Opposition leader Steven Marshall said.

But Senator Xenophon said South Australia would still be below Victoria and New South Wales, which have more than 45,000 voters per electorate.

"Currently, federal electorates have over 100,000 voters in them. This proposal would still mean that those [state] electorates would be about a third of the size of those federal electorates," Senator Xenophon said.

"If federal regional MPs can service their electorates, well there's no reason why a state MP can't do the same."

He denied it was a political manoeuvre to ensure more support for his party.

But the Opposition has described it as a cheap shot at politicians who worked hard.

The South Australian election will be held in March.

Nick Xenophon will run in the seat of Hartley.