Japan's current account surplus - the difference between its export and import of goods and services - rose by 6.5% year on year in September.
High oil prices hit Japan in August
It increased to 1.86 trillion yen ($15.73bn; £8.99bn), thanks to income from overseas investments offsetting a narrowing trade gap.
The official figures from the Japanese Ministry of Finance were better than market expectations.
Analysts had been expecting a slight year on year fall of 2.6%.
The investment income surplus was up 33.5% on the year to 1.013 trillion yen; while the surplus in trade in goods and services fell to 862.7bn yen.
August's overall current account surplus figure fell by 15.6% due to a peak in oil prices, but the global cost of crude has since fallen back.
Japan's economy expanded at a faster-than-expected pace in the third quarter, boosted by strong domestic demand, official figures showed last week.
Japanese gross domestic product (GDP) rose by 0.4% in the three months to September, the Cabinet Office said.
That brought Japan's growth rate for the year to an annualised 1.7%, well above forecasts for a figure of 1%.
Analysts said the pace of growth would help ease deflation, which has gripped the economy for more than seven years.