In a Realmeter poll of some 1,012 people nationwide surveyed last week and released on Monday, only 17.3 percent of respondents said Yoon is doing a good job, down 7.7 percentage points from a week earlier.
After his aborted martial law gambit last week, his disapproval rating rose to 79.2 percent, up 8.2 percentage point from the previous week.
Yoon's approval rating plummeted across all age groups except for those in their 20s, who showed a slight increase of 1.2 percentage points.
His approval rating, in particular, fell by more than 10 percentage points among conservative supporters of the ruling People Power Party (PPP) in its traditional strongholds of Busan and Daegu in Gyeongsang provinces.
Support for the PPP dropped to 26.2 percent, down 6.1 percentage points from the previous week, while the main opposition Democratic Party (DP) saw its support rise by 2.4 percentage points to 47.6 percent.
The pollster said the 20-percent gap between the two parties is the largest since his inauguration in 2022.