The main purpose of this study was to reveal the adult students' composite structure of dispositional optimism/pessimism, and relationship between adult students' dispositional optimism/pessimism and psychological well-being. 580 college adult students were assessed with dispositional optimism/pessimism scale and psychological well-being scale. The obtained data were analyzed by structural equation modeling. The results showed that structure of adult students' dispositional optimism/pessimism was composed of dispositional optimism and dispositional pessimism, and there were significantly correlations between adult students' dispositional optimism/pessimism and psychological wellbeing. Based on the findings, suggestions for future studies are provided.