The nation's foreign-exchange reserves totaled $817.95 billion in June, up $1.10 billion from the previous month due to investment returns from foreign bonds, mainly U.S. Treasuries, the Finance Ministry said Wednesday.
The figure was the second-highest on record, following the record $826.58 billion logged in March, the ministry said.
Japan remained the largest holder of foreign reserves of any country or territory for the 55th straight month, based on the latest comparable data.
It was the second straight month the reserves have increased, after they fell in April for the first time in eight months as Japanese monetary authorities stopped dollar-supporting currency operations in March.
The absence of foreign-exchange intervention caused "a slight drop" in the reserves for June, but that was more than offset by investment returns from foreign bonds, as was the case for May, a ministry official told reporters.
Japan has taken a hands-off approach to the yen since March 17, when it ended a 15-month intervention campaign to keep the currency from rising too fast and harming the export-driven economic recovery.
Foreign exchange reserves consist of securities and deposits denominated in foreign currencies plus International Monetary Fund reserve positions, IMF special drawing rights and gold.
Japan had $658.11 billion in foreign securities at the end of June, up from $637.81 billion in May.
It had $140.51 billion in foreign currency deposits, down from $159.34 billion.
Of the deposits, $6.31 billion was held in foreign central banks and the Basel-based Bank for International Settlements, $51.69 billion in Japanese banks and $82.51 billion in foreign banks.
Japan had $9.74 billion in gold, up from $9.68 billion in May.
It had $6.93 billion in IMF reserve positions, down from $7.35 billion, and $2.67 billion in special drawing rights, down from $2.68 billion.