This study aimed to verify the relationship between the level of understanding of health information and health behaviors among Korean adults. In total, 228 984 adults who participated in the 2021 Korea Community Health Survey were included. Participants were divided into three groups according to age (19–44, 45–64 and 65+). The ability to understand verbal and written health information was included, and its association with health behaviors, including smoking, alcohol consumption and preventive health service uptake, was assessed. Associations between the ability to understand health information and health behaviors were analyzed using chi-squared tests and multiple logistic regression analyses. Approximately 22.7% and 20% of the participants responded that verbal and written health information were easy to understand, respectively, with significant differences by age group. Compared to those with easy-to-understand verbal health information, those with difficulty in understanding had a higher risk of current cigarette smoking and monthly drinking and were less likely to engage in more than moderate physical activity, walking, influenza vaccination in 1 year, cancer examination in 2 years and medical examination in 2 years. Difficulty in understanding or no interest in written health information was also associated with unhealthy behaviors. A strong ability to understand health information is related to positive health behaviors. However, there are differences in the associations by age group, which should be considered when establishing a health literacy improvement strategy. These findings could promote health literacy and ultimately contribute to helping individuals make better choices for positive health behaviors.