The value of bonds sold in Asia's fourth-largest economy came to 57.5 trillion won ($48.3 billion) last month, down 9.6 trillion won from a month earlier, according to the data from the Korea Financial Investment Association.
Last month's drop compares with a 1 trillion-won on-month decrease recorded in August.
Sales of state and financial bonds sank by 9.7 trillion won and 3.7 trillion won from August, respectively, while corporate bond sales grew by 4.6 trillion won.
The issuance of environment, social and governance (ESG) bonds expanded by 300 billion won to 7.4 trillion won.
ESG bonds are a type of sustainability debt offering aimed at financing corporate activities in environmentally friendly and sustainable projects.
Foreign investors bought a net 9.1 trillion won worth of South Korean bonds in September, with their holdings of local bonds hitting an all-time high of 203.6 trillion won.
As of end-September, the value of outstanding bonds in the country reached 2,434 trillion won, down 2.2 trillion won from the previous month, according to the data. (Yonhap)