Previous research has shown that personality traits are associated with self-reported health status in the general population. COPD Assessment Test (CAT) is increasingly used to assess health status such as the impact of chronic obstructive pulmonary disease (COPD) on patients' daily life, but knowledge about the influence of personality traits on CAT score is lacking. The aim of this study was to examine the influence of Big Five personality traits on CAT score and the relation between personality traits and mental symptoms with respect to their influence on CAT score. A sample of 168 patients diagnosed with COPD was consecutively recruited in a secondary care outpatient clinic. All participants completed CAT, NEO Five-Factor Inventory, and Hospital Depression and Anxiety Scale. Multiple linear regression analysis was used to explore the association between personality traits and CAT scores and how this association was influenced by mental symptoms. The personality traits neuroticism, agreeableness and conscientiousness; and the mental symptoms depression and anxiety showed significant influence on CAT score when analysed in separate regression models. Identical R-square (R = 0.24) was found for personality traits and mental symptoms, but combining personality traits and mental symptoms in one regression model showed substantially reduced effect estimates of neuroticism, conscientiousness and anxiety, reflecting the strong correlations between personality traits and mental symptoms. We found that the impact of COPD on daily life measured by CAT was related to personality and mental symptoms, which illustrates the necessity of taking individual differences in personality and mental status into account in the management of COPD.