This study aimed to conduct importance-performance analyses (IPAs) based on Korean middle school students’ health management awareness during the post-coronavirus disease 2019 (COVID-19) era. Data were collected from 867 Korean middle school students (13–15 years old) via online and offline surveys between May and June 2023. Frequency analysis, reliability analysis, IPA based on the entire student group, and IPA depending on sex were carried out with the collected data, which revealed the following. First, regardless of sex, the IPA results indicated that four factors of mental health were located in the third quadrant, with one factor of the same variable in the fourth quadrant. The three factors of disease management were located in the third quadrant. Regarding physical activity, two factors were located in the first quadrant, one in the second quadrant, and one in the third quadrant. Regarding sleep management, two factors were located in the second quadrant, one in the third quadrant, and one in the first quadrant. Regarding eating management, two factors were located in the third quadrant and one in the fourth quadrant. Regarding the social distancing variable, all four factors were located in the third quadrant. Regarding hygiene management, two factors were located in the first quadrant, one in the third quadrant, and one in the fourth quadrant. Furthermore, the IPA results indicated sex differences in regular sports and vigorous movement activities associated with physical activity. Additionally, a sex difference was observed in regular diet associated with eating management. This study proposed possible measures for encouraging middle school students to recognize the importance of health and increase their health-related performance during the COVID-19 endemic phase.