Singapore banks remain among the strongest in the world, but all three slipped down the league table in an annual survey conducted by Bloomberg Markets magazine.
OCBC was the highest-ranked local lender, coming in at fourth, down from its second placing in last year's list.
It was the top-ranked Singapore bank in the same survey in 2010 and 2011.
DBS dropped to seventh place from fifth last year while United Overseas Bank fell six notches to 12.
The survey looked at banks with at least US$100 billion (S$125 billion) in assets as of May 1, taking into account five criteria, including Tier 1 capital compared with risk-weighted assets and non-performing assets against total assets.
Other criteria were the ratio of non-performing assets to total assets, the ratio of reserves for loan losses to non-performing assets, the ratio of deposits to funding and the efficiency ratio, which compares costs with revenue.
Hong Kong's Hang Seng Bank rose nine places in the survey to rank as the world's strongest bank.
The lender, which is majority-owned by London-based HSBC Holdings, has expanded rapidly at home and in mainland China and is the second biggest retail bank in Hong Kong.
Its assets stood at HK$1.14 trillion (S$225 billion) as of the end of last year.
Bloomberg Markets reported that Hang Seng Bank has been building up its risk buffers since 2009, in part by paring dividends.
It is doing this to prepare for the more stringent regulatory requirements being phased in by the Hong Kong Monetary Authority to comply with Basel III international guidelines.
Private banks were included in the survey for the first time this year, with two lenders making it into the top three.
Canada's Desjardins Group, an alliance of credit unions, and Tokyo-based Norinchukin Bank, a cooperative that serves 3,800 farm, fishing and forestry cooperatives, were joint second on the list.
Their business models are different from commercial lenders, which may have given them the slight edge.
The Straits Times understands that their main assets are government bonds and securities, unlike commercial lenders whose main assets are savings deposits that may pose a higher risk.
OCBC chief financial officer Darren Tan said yesterday: "We actively manage our capital and liquidity positions to ensure that they remain at prudent levels to support the bank's business growth."
A DBS spokesman said Singapore banks consistently remain among the strongest in the world, as underlined by different rankings.
"As an example, DBS has been named Asia's safest bank by Global Finance for five consecutive years from 2009 to 2013."
Mr Jimmy Koh, UOB's head of investor relations, said the bank believes in a disciplined approach to growth. "We focus on building balance sheet strength as well as generating risk-adjusted returns."