Introduction: The psychological impact of experiencing the pandemic of COVID-19 on the general population is not yet fully evidenced. The same occurs when analyzing the issue in specific audiences, such as adolescents. Goals: This study aimed to identify self-care behaviors and feelings of Brazilian adolescents during one of the moments of the COVID-19 pandemic. Methods: This is a qualitative study with the participation of nine adolescents from a public school. The data were collected using the diary technique. Diaries prepared by the researchers were filled out individually by the adolescents for 30 days. The data were treated descriptively and according to the assumptions of thematic analysis. Results: Two themes were constructed in the data analysis: 1) Understanding of self-care and mental health; 2) Experiences of self-care. Participants were found to have a good understanding of mental health and the need to adopt self-care behaviors during the COVID-19 pandemic. Journal entries revealed practices of physical activity, balanced and healthy eating, as well as seeking specialized support or from friends. Negative, but also positive feelings and aspects were mentioned by the participants as related to the pandemic moment. From the records, it was verified that stress control measures, eating habits, virtual communication and moments of reflection were care measures to control the negative feelings or experiences during the data collection period. Conclusions: The results obtained reveal that the methodology used - journaling technique - allowed the participants to record their routine and, at the same time, reflect on the moment they were experiencing. These aspects are important in that the pandemic had not yet been overcome at the time of data collection and few studies had verified the behaviors and feelings of adolescents. [ABSTRACT FROM AUTHOR]