The Nikkei stock average ended 3.1 percent higher, pushing the yen lower. The dollar was up almost 0.4 percent over 102 yen, having hit a February high of 102.7, while the euro was up a full percent at 141.
Still, some market participants used the BOJ's announcement as an excuse to buy back dollars after the U.S. currency's recent decline. The latest easing by the BOJ comes nearly a year after it unleashed a massive bond-buying program aimed at getting the economy out of years of deflation.
The highlight of the European session was the euro hitting a five-week high against the Swedish crown of 8.9 crowns after consumer prices in Sweden fell more than expected in January and revived talk of an interest rate cut.
The euro also rose against the British pound to trade near 82 pence after softer-than-expected UK inflation data. The single currency's gains across a host of currencies propped it up against the U.S. dollar, too.
The euro rose to near $1.37 against the dollar, not far from its Jan. 24. high which for now was also acting as a key resistance. The euro barely reacted to a mixed German ZEW survey.
The Australian dollar slipped from a one-month high of $0.91 to trade lower on the day at $0.90. It eased after China's central bank drained funds from the market and signaled a continuation of its tight liquidity policy aimed at managing a slowdown in the world's second-largest economy.
The Aussie is often used as a more liquid proxy to investments in China. Earlier, in minutes released on Tuesday of the Reserve Bank of Australia's Feb. 4 meeting, when the RBA surprised some by dropping its bias to ease further, the central bank noted that a lower exchange rate would support growth.