Standard and Poor's says New Zealand's banking system remains relatively low-risk, despite its reliance on offshore funding.
The agency's Banking Industry Country Risk Assessment (BICRA) methodology evaluates and compares global banking systems using economic and industry risk factors - ranking them from one to 10.
New Zealand's rating has slipped from two to three, and it now sits alongside nations like Italy, Korea, the US and the UK.
Standard and Poor's says the whole system's methodology has changed, but New Zealand remains at the low-risk end of the scale.
Credit analyst Sharad Jain says net offshore borrowing by New Zealand banks is a key weakness based on the view that a banking system dependent on offshore borrowings is at greater risk of disruption.
Mr Jain says the risks could include problems with the banking system itself, or problems elsewhere in the global financial system, for example the situation with the European sovereign market, which has the potential to disrupt access to funding.
He says the BICRA system does feed into bank's individual ratings, but a lower country score doesn't mean a lower rating for banks.
Mr Jain says Standard and Poor's expects to complete its ratings review of the major banks by the middle of December.