The Korea Institute for Health and Social surveyed 7,000 adults last August and September.
According to the report, published in December, 34.7 percent of respondents were under high stress, and 3.2 percent were under extremely high stress, meaning a total of 37.9 percent of were significantly stressed.
Another 56.2 percent said they were under moderate stress, meaning that more than 90 percent of Korean adults experience some level of stress daily.
Only 5.9 percent said they were mostly free from stress.
"This indicates that Korean adults experience a lot of psychological pressure due to (the highly competitive process of) seeking jobs, or conflicts in the workplace or within the family," the researchers said.
The survey results showed that men, people earning high incomes, and double-income couples tended to be more stressed than their counterparts.