The aim of this study is to screen the cognitive function during exacerbation of chronic obstructive pulmonary disease (COPD) and investigate whether there is any association between cognitive function and functional impairment, disease severity, or other clinical parameters. Age and sex-matched 133 subjects with COPD exacerbation, 34 stable COPD subjects, and 34 non-COPD subjects were enrolled in this study. For the purpose of this study, mini-mental state examination (MMSE) and Hospital Anxiety and Depression scale were performed. Six-minute walk distance (6MWD) was recorded, and BODE index was calculated. COPD subjects with exacerbation had the lowest MMSE scores (p = 0.022). Frequency of subjects with MMSE score lower than 24 is 22.6, 8.8, and 8.8% in the COPD subjects with exacerbation, stable COPD, and non-COPD control subjects, respectively. The COPD subjects with exacerbation who had MMSE scores lower than 24 were older and less educated. Subjects with COPD exacerbation had shorter 6MWD than that of stable COPD and non-COPD subjects. After controlling for the impact of age and educational level on MMSE, there was no association between 6MWD and MMSE scores in subjects with COPD exacerbation. Cognitive impairment is an important comorbidity during COPD exacerbation. Functional capacity is also lower in exacerbation. However, no association was found between cognitive impairment and functional capacity during exacerbation.