South Korea's terms of trade fell for the sixth consecutive month in September due to a rise in prices of imported goods, central bank data showed Thursday.

The nation's net terms-of-trade index for goods -- a gauge of overall trade terms -- declined 4.5 percent last month from a year earlier, according to preliminary data from the Bank of Korea (BOK).

The figure is calculated by dividing the index for export prices by that for import prices. It shows the amount of imports a country can buy for each unit of exports and the base year is 2015, with a benchmark index of 100.

Last month, the index for customs-cleared export prices went up 18.4 percent from the previous year, marking the 11th straight month of increase.

The index for import prices surged 33.8 percent from a year earlier due to rising crude and raw material prices. (Yonhap)