The bank said it would boost its asset buying fund by 5.0 trillion yen to 55 trillion yen ($723 billion), with the extra amount earmarked for the purchase of Japanese government bonds.
It also said its policy board voted unanimously to keep its key interest rate unchanged between zero and 0.1 percent.
The yen was barely changed at 76.00 to the dollar after the announcement compared to 76.03 yen beforehand.
The bank's asset purchase fund is a key policy tool it uses to buy Japanese government bonds, corporate bonds and exchange traded funds.
The expansion follows the BoJ's August move to expand the scheme to buy securities and boost liquidity to 50 trillion yen amid worries over the strong yen, in tandem with a government market intervention in a bid to weaken the unit.
"Although an adverse effect from a slowdown in overseas economies and the appreciation of the yen will continue for the time being, Japan's economy is expected to return to a moderate recovery path," the BoJ said in a statement.