The nation's foreign currency reserves totaled $363.69 billion as of the end of February, down by $529 million from the previous month, the Finance Ministry said Wednesday.
The figure, which follows January's increase of $2.58 billion from December, marked the first decline in the currency reserves since August, the ministry said.
The ministry cited the weakening of the euro against the dollar as a major contributing factor for the February drop.
The euro fell 1.4 percent against the dollar from $0.9367 at the end of January to $0.9234 at the end of February, reducing the value of the nation's non-dollar denominated assets, the official said.
Japan remained the top holder of foreign currency reserves for 15 months in a row as of the end of December, compared with any country or territory, the official said.
The foreign currency reserves include reserves of convertible foreign currencies in the form of securities and deposits, gold and International Monetary Fund special drawing rights.