Trade was muted ahead of a key policy decision by the US Federal Reserve, while dealers also had an eye on the release of corporate results in Japan, which began after the market closed.
Tokyo gained 1.39 percent, with the Nikkei up 133.15 points to 9,691.84.
South Korean shares closed flat, trimming earlier gains, with the benchmark KOSPI up 0.40 points at 2,206.70.
Sydney ended 0.83 percent weaker on concerns over falling metals prices and higher inflation, analysts said. The S&P/ASX 200 was down 40.9 points at 4,872.9. Consumer price rose 1.6 percent quarter-on-quarter in March, above estimates of a 1.2 percent spike, and jumped 3.3 percent from a year earlier.
Hong Kong was 0.41 percent higher by the break while Shanghai rose 0.17 percent in afternoon trade.
Investors around the region took their early trading cues from Wall Street where the Dow jumped 0.93 percent to a near three-year high on Tuesday following more strong earnings reports from corporate America.
The tech-rich Nasdaq Composite gained 0.77 percent and the S&P 500, a broad measure of the markets, added 0.90 percent.
Ratings agency Standard & Poor's downgraded its outlook on Japan's debt to negative from stable, citing the impact of last month's devastating earthquake-tsunami and the resulting nuclear crisis.
It also said the cost of rebuilding could range from 20 trillion yen to 50 trillion yen ($245 billion to $612 billion).
"Standard & Poor's expects costs related to the March 11, 2011, earthquake, tsunami, and nuclear power plant disaster will increase Japan's fiscal deficits above prior estimates by a cumulative 3.7 percent of GDP through 2013," it said in a statement.
The news initially sent the dollar rallying against the yen before easing slightly.
The greenback was at 81.74 yen in Tokyo afternoon trade, slightly up from 81.55 in New York late Tuesday. The euro was at $1.4675 from $1.4636 while the single currency rose to 120.00 yen from 119.38 yen.
Japanese investors were also watching earnings reports from big firms, which are expected to give an indication of the economic impact of last month's disasters.
Automaker Mitsubishi said its on-year profits to March more than tripled to 15.6 billion yen, but added it was not able to produce "rational forecasts" for earnings outlook because of the effect of the disaster.
Although the US Fed is expected to keep interest rates at record lows after its two-day meeting on Wednesday, the key point of interest is whether it will keep its loose monetary policy, known as quantitative easing, in place.
On oil markets New York's main futures contract, light sweet crude for June, was down 19 cents at $112.02 a barrel, while Brent North Sea crude for delivery in June eased 22 cents to $123.92.
Gold opened at $1,508.00-$1,509.00 an ounce in Hong Kong, down from Tuesday's finish of $1,504.00-$1,505.00.
In other markets:
-- Taiwan's weighted index rose 101.11 points or 1.13 percent to 9,049.25.
Taiwan Semiconductor Manufacturing Company rose 2.84 percent to Tw$72.3 while Hon Hai was 0.46 percent higher to Tw$109.0.
-- Wellington rose 0.16 percent, or 5.56 points, to 3,492.04.
Market heavyweight Fletcher Building fell 0.6 percent to NZ$9.14 and Air New Zealand was steady on NZ$1.11.
-- Manila closed 0.36 percent, or 15.75 points, higher at 4,321.32.
The most active stocks included Alliance Global, which was up 1.5 percent at 11.98 pesos while DMCI Holdings was off 2.3 percent at 45.90 and First Gen rose 3.7 percent to 14.52.