It is the fastest on-year decline since October 2011, when the index lost 11 percent.

The index measures the amount of imports a country can purchase for each unit of exports. A reading below 100 means import prices are higher than those of exports, resulting in unfavorable terms of trade.

The BOK explained that the steep drop in the trade terms index was led by rising oil prices, as South Korea imports most of its crude oil demand.

Prices of Dubai crude, South Korea's benchmark, soared 42.9 percent on-year in October.

"In November, the oil prices started to decline. The November price will be reflected in the December trade terms index," a BOK official said.

Income terms of trade, which gauge the total amount of goods that a country can buy for its total exports, also fell 8.3 percent on-year to a nine-month low of 144.68 last month.

The index of exports volume climbed 2.9 percent on-year to 159.88 in November, slowing down from a 25.8 percent on-year gain in the previous month.

The imports volume index edged up 0.4 percent to 136.05 last month, the data showed. (Yonhap)