The BOK attributed the drop to the advance of the US greenback against other currencies.
"This (drop) was mainly due to a cut in the dollar value of other foreign denominated assets caused by the strengthening of the US dollar," it said.
At the end of February, the dollar traded at about $1.289 per British pound, up 1.5 percent from $1.309 per pound a month earlier, the BOK said in a press release.
The dollar also jumped 2.1 percent against the Australian dollar over the cited period, fetching $0.6579 per Australian dollar at end-February instead of $0.6718 at end-January.
As of end-February, South Korea held $371.22 billion in foreign securities, down $7.23 billion from a month earlier.
Its foreign savings, on the other hand, jumped $6.8 billion over the cited period.
Foreign exchange reserves also include special drawing rights, gold bullion and the International Monetary Fund (IMF) reserve position.
The country's gold holdings remained unchanged at $4.79 billion, while its special drawing rights slipped $60 million to $3.27 billion.
South Korea's FX reserves are the world's ninth largest. (Yonhap)