The strong relationship between sleep and health is defined in the literature. While the need for sleep increases in adolescence with the effect of physiological and hormonal changes, the studies have highlighted the serious sleeping problems of adolescents compared to childhood and adulthood. This study aimed to examine the relationship between chronotype, bedtime, sleep quality and mental health among adolescents. This research was a descriptive-relational study. A total of 1083 students constituted the group of the research. The data were collected through the Morningness-Eveningness Questionnaire (MEQ) and General Health Questionnaire and a questionnaire consisting of some questions about sleep. In the evaluation of data, multiple regression, mediation and path analysis were performed. Age, having problems affecting sleep, difficulties falling asleep, sharing the room with someone else and lack of leisure activities were related to bedtime. It was found that determinants of sleep quality were the variables related to sleep itself. Being a male student, having problems affecting sleep, difficulties falling at sleep, waking up during the night, getting support in the morning for waking up and lack of leisure activities negatively affected mental health. MEQ scale was interpreted as a determinant of sleep time, sleep quality, and mental health level. Although the MEQ score directly affected sleep quality, bedtime had a partial mediation role between MEQ score and sleep quality. Sleep quality had a full mediation role between MEQ score and mental health score. School health workers, especially nurses, should consider chronotype-focused measures to improve adolescents’ sleep quality and psychosocial health.