Credit Suisse faced the largest downgrade of all of the 15 banks affected, with its rating slashed three levels from Aa1 to A1.
UBS is disappointed at having had its rating revised from Aa3 to A2, spokeswoman Dominique Scheiwiller told online news site Basler Zeitung.
Moody’s nevertheless confirmed that the outlook for both Swiss banks was stable, and referred to the strength of the Swiss franc as well as Switzerland’s minimal engagement with countries most deeply affected by the Euro crisis, news site NZZ Online reported.
The shares of both banks fell slightly on Friday morning following the announcement.
Some of the biggest names in banking -- including Goldman Sachs, Barclays, Citigroup, HSBC and Deutsche Bank – also saw their ratings slashed Thursday, spelling increased investor scrutiny and potentially higher borrowing costs.
"All of the banks affected by today's actions have significant exposure to the volatility and risk of outsized losses inherent to capital markets activities," said Greg Bauer, Moody's global banking managing.
In total four firms were downgraded by one notch, 10 firms by two notches and one by three notches.
Holding companies of a number of the same banks were also downgraded.
Under-pressure US banking giant Morgan Stanley was seen as winning a partial victory by only receiving a two-notch downgrade.
Morgan Stanley welcomed the partial reprieve, but nevertheless questioned the Moody's decision.
"While Moody's revised ratings are better than its initial guidance of up to three notches, we believe the ratings still do not fully reflect the key strategic actions we have taken in recent years," it said in a statement.
Ratings agencies like Moody's were pilloried for failing to predict the cataclysm that engulfed Wall Street and the world beginning in 2008, and Thursday's move was part of a sector-wide effort to tighten up ratings.
But even so, the swathe of downgrades amounts to a fresh indictment of the health of the global financial system, which has seen wave after wave of crisis over the last four years.
Since the sub-prime crisis banks have seen the value of their assets slump and their access to capital shrink, which has repeatedly forced taxpayers and central banks to step in to provide liquidity.
Many governments have been forced to provide bailouts, straining already precarious public finances.
On Thursday Spain became the latest to signal a bank bailout.
Madrid announced that its crisis-torn banks need up to 62 billion euros ($78 billion) to survive. It is expected to formally ask its eurozone partners for the cash on Friday.
The 15 banks downgraded were: Bank of America, Barclays, Citigroup, Credit Suisse, Goldman Sachs, HSBC, JPMorgan Chase, Morgan Stanley, Royal Bank of Scotland, BNP Paribas, Credit Agricole, Deutsche Bank, Royal Bank of Canada, Societe Generale and UBS.
Moody's began its review of the banks in February, and the move was widely anticipated, helping to send the Dow Jones Industrial Average sharply lower on Thursday.