South Korea's foreign reserves increased for a second straight month in July as the US dollar's fall boosted the conversion value of holdings in other currencies and increased investment returns, central bank data showed Thursday.

The country's foreign reserves came to $421.80 billion as of end-July, up $350 million from the previous month, according to the data from the Bank of Korea.

The dollar's slide last month boosted the converted value of holdings denominated in other currencies, the BOK explained.

The dollar index that gauges the greenback's value against major peers fell 1.7 percent last month, the central bank said.

Foreign reserves consist of securities and deposits denominated in overseas currencies, International Monetary Fund reserve positions, special drawing rights and gold bullion.

Foreign securities, such as US Treasuries, had been valued at $376.53 billion as of end-July, up $890 million from a month earlier. They accounted for 89.3 percent of foreign reserves, the data showed.

The value of deposits stood at $20.96 billion at the end of July, down $600 million from a month earlier.

South Korea ranked as the world's eighth-largest holder of foreign reserves at the end of June, the BOK said. (Yonhap)