Emotional variability has been posited as a risk factor for adolescent psychopathology. However, it is unclear whether parent emotional variability may also function as a risk factor that heightens adolescent mental health problems. To fill this gap, the present study examined whether parent and adolescent emotional variability in both positive emotion (PE) and negative emotion (NE) is associated with adolescent psychopathology and potential sex differences in these associations. Participants were 147 adolescents and their parents in Taiwan who completed a baseline assessment, a 10-day daily diary study, and a 3-month follow-up assessment. The results indicated that parent NE variability was associated with risk for adolescent internalizing problems and depressive symptoms, after accounting for baseline levels, adolescent NE variability, parent internalizing problems, and mean levels of parent and adolescent NE. Adolescent PE variability was also associated with the risk for adolescent externalizing problems. Furthermore, higher parent PE variability was associated with more internalizing problems only for female but not male adolescents. The findings highlight the importance of assessing emotion dynamics in both parents and adolescents to better understand the development of adolescent psychopathology.