Objective Society’s sleep-wake cycle and eating behaviors have altered and are considered the psychological outcomes of the coronavirus disease-2019 (COVID-19) pandemic. Our aim was to examine the relationship between sleep-wake rhythms, eating behaviors (dieting, oral control, and bulimic behaviors), and attention deficit hyperactivity disorder (ADHD) symptoms with weight gain during the COVID-19 pandemic. Methods The participants were 578 female university students divided into three groups based on weight change during COVID-19 who lost weight, whose weight did not change (nWC), and who gained weight (WG). The participants’ information about weight change in the last year and responses to the Pittsburg Sleep Quality Index, Eating Attitudes Test, Adult ADHD Severity Rating Scale, and Wender Utah Rating Scale were collected via an online survey from January 8, 2021 to January 11, 2021. Results The sleep-wake phase was more delayed in WGs than in the other two groups. The bulimic behavior score was higher and the oral control behavior score was lower in the WG group than in the nWC group. A hierarchical regression analysis model, in which weight change scores were dependent variables, showed that mid-sleep time in second step (β=4.71, t=2.18, p=0.03), and oral control (β=-0.11, t=-3.24, p=0.001)/bulimic behaviors (β=0.20, t=3.20, p=0.001) in third step were associated with weight change after controlling for both current and childhood ADHD symptoms. Conclusion Chronotherapeutic approaches that regulate sleep-wake rhythm may facilitate weight control of individuals during stressful periods, such as the COVID-19 outbreak.