South Australia credit rating improves

South Australia's long-term credit rating has been lifted to AA+ by ratings agency Standard & Poor's.

The agency says the improvement from AA is based on the state's stable economic outlook and the expectation of sustained budget surpluses.

"An upgraded credit rating to AA+ sends a clear message to global markets and potential investors that South Australia is open for business," SA Treasurer Rob Lucas said on Friday.

Mr Lucas said the increase also backed the state's focus on better services, lower costs and job creation.

Earlier this month, the treasurer delivered the new government's first budget, which forecasts a modest $48 million surplus for 2018/19, rising to $211 million by 2021/22.