The Finance Ministry said Friday the 1.5 percent month-to-month decline resulted largely from the euro's depreciation against the U.S. dollar, due to the European sovereign debt crisis and the falling gold prices.
It was the first such decline in three months, Kyodo News reported.
Japan's reserves are exceeded only by those of China, whose reserves total more than $3 trillion.
The Japanese government has been trying to check the appreciation of its yen, as a higher yen makes its goods more expensive, adversely affecting its export-dependent economy. The government and its central bank intervened in the currency market in August but the yen has continued to appreciate.