Objectives: This study sought to reveal changes in the prevalence of metabolic syndrome between before and after the start of the coronavirus disease 2019 (COVID-19) pandemic and to identify the group showing the greatest change.Methods: We compared the prevalence of metabolic syndrome between 3 years before the COVID-19 pandemic and soon after the initial outbreak of COVID-19 in 2020 among 24,564 adults ≥19 years of age using data from the Korea National Health and Nutrition Examination Survey. Results:The prevalence of metabolic syndrome increased steadily between 2017 and 2020 (29.4% to 35.3%, P for trend < 0.001), with annual percent changes of 2.0%p, 2.2%p, and 1.7%p, respectively. Changes in prevalence after the COVID-19 outbreak compared to 3 years before the COVID-19 pandemic showed a significant increase in men (6.2%p; 95% confidence interval [CI], 3.5-8.9) compared to women (1.5%p; 95% CI, −1.2 to 4.1).The age groups with the most significant increase in metabolic syndrome prevalence after the COVID-19 pandemic were those in their 40s (4.6%p; 95% CI, 0.9-8.4) and 50s(5.8%p; 95% CI, 2.2-9.4). By education background, the increase in metabolic syndrome prevalence was greatest among those with a college degree or higher (5.1%p). According to income, the prevalence of metabolic syndrome in high-(5.3%p) and low-income (4.6%p) groups increased statistically significantly. Conclusion:The increasing trend in the overall prevalence of metabolic syndrome continued after the COVID-19 pandemic. However, the prevalence of metabolic syndrome among adult men in their 40s and 50s changed significantly after the COVID-19 outbreak in Korea.