Background We investigated the association between cognitive dysfunction (CD) and chronic obstructive pulmonary disease (COPD) during exacerbation and compare with stable COPD patients and control subjects. Also, we compared the cognitive function of long-term oxygen therapy (LTOT) dependent patients and not receiving LTOT. Methods The 121 people included in the study. They were divided into three groups: exacerbation of COPD (COPD-E), stable COPD (COPD-S) and control groups. Also, COPD patients were divided into two groups, non-user LTOTD-COPD and regular-user LTOTD-COPD. The patients were asked in their native language by exact conversion of the questions of MMSE (Mini Mental State Examination). Results The mean age of patients was 67 and ratio of patients with MMSE results below 24 was 41.6%. MMSE score was 18.9 in patient with exacerbation and 25.7 in stable COPD. Age average was higher and MMSE was lower in COPD-E group. Low educational degree was predicting factor for CD in COPD-E group. Low MMSE was related with decreased FEV1%, pO(2)and sO(2)values, increased pCO(2)values, low educational level and increased comorbidity. MMSE score was 18.8 in reguler-user LTOTD COPD and 24.9 in nonuser LTOTD-COPD. Regular-user LTOTD-COPD groups exacerbation rate was higher than nonuser LTOTD-COPD group. Conclusion MMSE scores was low in COPD-E group and regular-user LTOTD-COPD group. This is important because MMSE identifies clinically significant CD. This suggests that the CD may be linked to the causes of severe exacerbations. Clinicians need to look for CD, because cognitive function needs to be taken into account in their management of the patient.