Objective: Dispositional characteristics like emotional stability and social cynicism have been consistently associated with negative affect, which is a known predictor and outcome of poor sleep quality. This study hypothesized a bidirectional relationship of sleep quality with emotional stability and social cynicism over a five-year period. Methods: Participants were 7,181 Chinese people, who completed two waves of online surveys from a larger panel study. Questionnaires on Big Five personality traits, social cynicism, and sleep quality were administered twice at a five-year interval. Results: Cross-lagged analysis revealed a significant bidirectional relationship between emotional stability and sleep quality over five years as hypothesized. However, there was no association between sleep quality and social cynicism in either direction. Conclusion: Our study provides consistent evidence of a bidirectional relationship between sleep quality and emotional stability in a five-year time-frame among a younger population (mean age = 24.86). Given the critical role of emotional stability in various areas of functioning, the findings highlight the importance of sleep health education in young adults, who are going through a critical period of personality development.