The weakness lay not in participation but in the size of the bids, as 15 institutions took part, one more than in July, even as their combined orders fell 41.2 percent.
The BOK received 500 billion won in bids for 700 billion won ($494 million) of one-year Monetary Stabilization Bonds, producing a bid-to-cover ratio of 71.4 percent, according to the auction results.
It awarded 410 billion won to 12 institutions at a yield of 3.350 percent, leaving the final issuance at 58.6 percent of the planned amount.
Bids ranged from 3.150 percent to 3.450 percent, with no partial award.
At the July auction, 14 institutions submitted 850 billion won of bids for the same 700 billion won offering, allowing the BOK to issue the full amount at 3.370 percent.
The average bid per participating institution therefore fell 45.1 percent in one month to 33.3 billion won from 60.7 billion won.
An AJP review of 339 one-year MSB auctions since 2010 found Wednesday's bid ratio was the eighth lowest over the period and the weakest since March 2024.
It was also the third undersubscribed auction in the past 12 months, following bid ratios of 97.1 percent in September 2025 and 77.1 percent in October.
A 2021 Capital Market Research Institute study found that one-year MSB auctions recorded an average bid ratio of 222.6 percent over the preceding decade and fell short of planned issuance in only 5.3 percent of cases.
Part of the latest decline may reflect the larger offering, as the BOK raised planned one-year issuance from 500 billion won in June to 700 billion won in July and August.
That explanation is limited, however, by the July comparison, when the same amount attracted 350 billion won more in bids.
The result points most directly to a pricing gap between the return investors required and the yield the central bank was prepared to accept.
The 3.350 percent accepted yield was the cutoff for the 410 billion won awarded, rather than the market-clearing yield for the entire 700 billion won offering.
Even if the BOK had accepted every submitted bid, the auction would still have fallen 200 billion won short, suggesting that full issuance may have required a higher yield capable of drawing additional demand or a smaller offering.
The auction alone, however, cannot determine whether the gap reflected expectations of higher market rates, more attractive returns on competing short-term debt or constraints on institutions' investment capacity - according to the central bank.
The result came two days after the BOK announced changes intended to improve MSB liquidity, including extending the fungible issuance period for one-year bonds to three months from two and introducing benchmark issues from Aug. 31.
Because Wednesday's auction was conducted under the existing framework, sales after the changes take effect will provide the next test of whether greater tradability can revive demand or investors continue to require higher yields.
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AJP Takeaways
The bid ratio for the BOK's one-year Monetary Stabilization Bond fell to 71.4 percent, the lowest in 29 months and the eighth lowest among 339 auctions since 2010.
Participation rose to 15 institutions from 14 in July, but total bids dropped 41.2 percent and the average amount per participant fell 45.1 percent.
The auction points to a pricing gap rather than a broad market shock, with post-Aug. 31 sales set to test whether improved liquidity can restore demand without higher yields.
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