The current account -- the broadest measure of foreign trade in goods and services -- showed an unprecedented surplus of $52.4 billion in the six months to June, according to data from the central Bank of Korea.
The surplus for June also hit a record monthly high of $12.2 billion.
The data showed tumbling oil prices that hit multi-year lows since late last year helped push down the value of imports, widening the current account surplus despite falling exports.
Exports account for more than a half of the Asia's fourth-largest economy, which imports most of its energy needs from overseas.
The value of imports from January to June stood at $218.8 billion, down 18.3 percent from a year ago, with the value of crude oil imports falling more than 40 percent.
The imports of petrochemical products also dropped 50 percent from a year ago.
For June alone, the value of imports tumbled 17.3 percent on-year to $36.1 billion.
The value of exports meanwhile fell to $279 billion for January to July, down 10.6 percent compared to the same period last year.
Overseas shipments of the country's main export products such as cars and electronics products fell six percent and 23.6 percent, respectively, compared to the first half of 2014.
Citing sluggish exports and weak domestic spending, the central bank last month cut its 2015 economic growth forecast for the third time this year, from 3.1 percent growth to 2.8 percent.
It also cited the impact of the outbreak of the Middle East Respiratory Syndrome (MERS) that devastated local businesses during its peak in June.