The dollar was at about 79.90 in Tokyo afternoon trade ahead of the BoJ policy announcement and fell to 79.50 yen after the central bank announced yet more easy money to help boost the slowing economy.
The yen also firmed slightly against the euro after the bank's announcement.
The euro bought $1.2894 and 102.37 yen, compared with $1.2900 and 103.18 yen before the BoJ announcement, and against $1.2900 and 102.95 yen in US trade.
With the additional cash, the bank's asset-purchase programme stands at a total 91 trillion yen, up from 80 trillion yen.
Last month, it unveiled plans to expand the fund by 10 trillion yen following similar moves by its European and US counterparts.
Market traders had largely been expecting a similar sized move on Tuesday, with one strategist telling Dow Jones Newswires in advance that it would make little difference to the value of the yen.
Barclays Capital currency strategist Masafumi Yamamoto said in a note to clients the dollar's fall could be "due to disappointment by some traders who had expected an additional 15 to 20 trillion yen cash injection, or profit-taking".
But Daisuke Karakama, market economist at Mizuho Corporate Bank, noted the scale of monetary easing was slightly bigger than expected.
"Many people were voicing disappointment but I think it wasn't so bad," he said. "Given the dollar had risen so much since mid-October on the easing expectations alone, however, it was only natural that it dropped."
HiFX Senior Trader Stuart Ive said euro-dollar trading was likely to remain mostly rangebound in the Asian session due to a lack of data.
The dollar was mixed against other Asia-Pacific currencies.
It eased to 1,091.60 South Korean won from 1,096.15 on Monday, and to 9,605 Indonesian rupiah from 9,630 rupiah, while it was flat at Tw$29.25.
The greenback firmed to 41.30 Philippine pesos from 41.25 pesos, to 30.74 Thai baht from 30.70 baht, to Sg$1.2225 from Sg$1.2209 and to 54.18 Indian rupees from 53.84 rupees.
The Australian dollar fell to $1.0343 from $1.0361 while China's yuan was at 12.67 yen against 12.76 yen.