South Korean retail investors’ combined margin and securities-backed borrowing reached 58.7561 trillion won ($42.9 billion) at the end of last month, approaching the 59 trillion won threshold as government bond yields climbed domestically and across major markets. Margin loan balances jumped 14.92% from the previous month-end to 33.2527 trillion won ($24.3 billion), while securities-backed collateral loans rose 0.21% to 25.5034 trillion won ($18.6 billion). Although total borrowing remained below the 64 trillion won ($46.8 billion) recorded at the end of June, brokerages’ average rates reached 8.94% for 61–90 day loans and 8.14% for 16–30 day loans. Margin lending lets brokerages finance stock purchases, while securities-backed loans are secured by existing stocks or bonds. Rising benchmark funding costs can lift these rates and increase investors’ interest burdens. The 3-year, 10-year and 30-year South Korean government bond yields rose to 3.879%, 4.371% and 4.627%, respectively. The moves followed a second consecutive Bank of Korea rate increase on the 27th of last month, to 3.00% from 2.75%, and coincided with higher yields in the United States, Japan and other major economies. The U.S. 10-year Treasury yield reached 4.788% on the 1st local time, its highest since January 14, 2025, while Japan’s 10-year government bond yield exceeded 3% for the first time since September 1996. Analysts warn that concentrated margin exposure to Samsung Electronics and SK Hynix could intensify forced selling during a market decline. Foreign investors’ South Korean equity selling also accelerated, reaching net outflows of 9.814 trillion won in July and 12.017 trillion won in August. The resumption of U.S. airstrikes on Iran pushed October-delivery WTI crude futures up 5.2% to $90.22 a barrel, adding to inflation and rate concerns. Share buybacks by Samsung Electronics and SK Hynix may provide a temporary supply-demand cushion, with Kiwoom Securities estimating support could last until mid-October if the current pace continues.