Tokyo stocks jumped 3.13 percent by the close Tuesday after the Bank of Japan held off expanding its asset-buying programme, but said it would boost some lending schemes to stimulate borrowing.
The Nikkei-225 index soared 450.13 points to 14,843.24, scoring its biggest one-day points gain since August. The broader Topix index of all first-section issues was up 2.68 percent, or 31.95 points, to 1,224.00.
Wrapping up a two-day policy meeting, the BoJ said it would keep its massive easing programme in place, in line with expectations.
However, it also decided to double the amount available under loan schemes to banks in a bid to stimulate lending to firms and to finance growth-stoking projects such as environmental research and natural resources development.
The move sent the yen tumbling in forex markets, a plus for shares of Japanese exporters.
The unit changed hands at 102.66 yen in afternoon trade, up from around 101.95 yen before the BoJ decision.
"Obviously, the market welcomed the BoJ decision," said Kenzaburo Suwa, strategist at Okasan Securities.
"The fresh measures are unlikely to have a significant impact on the Japanese economy, but the market positively reacted to the fact that the Bank of Japan did take action," he added.
Tatsunori Kawai, chief strategist at kabu.com Securities, told Dow Jones Newswires that "there was a sense of relief among some that at least it (the BoJ) didn't sound a more sombre tone after yesterday's worse-than-expected GDP numbers."
A post-meeting statement saw the bank keep its view of the economy unchanged from last month, saying it "has continued to recover moderately" and exports have been gradually picking up.
The BoJ decision came a day after weak growth data exacerbated fears that an April sales tax rise will derail Prime Minister Shinzo Abe's bid to stoke growth after 15 years of deflation.
Data showed that while the world's number three economy grew 1.6 percent over 2013 -- its best performance in three years -- it slowed to 0.3 percent in the October-December quarter.
In share trading exporters benefitted from the sudden fall of the yen, with Sony closing up 3.60 percent at 1,780 yen and chip component maker Kyocera up 3.73 percent at 4,611 yen.
Renesas Electronics shot up 8.62 percent to 630 yen after the Nikkei economic daily reported the firm plans to start mass production of high-performance chips for automobile-control systems this year.