Abstract. The aim of the present study was to compare leptin and interleukin (IL)-6 expression in patients and rat models with chronic obstructive pulmonary disease (COPD). Leptin and IL-6 levels were determined in patients with an acute exacerbation of COPD (AECOPD), stable COPD and in healthy controls. Rat models of COPD were developed, histological and immunohistochemical analyses were performed and leptin and IL-6 levels were determined. Leptin and IL-6 levels in the serum and sputum were higher in patients with AECOPD compared with stable COPD and control patients. In rats, leptin and IL-6 were expressed in bronchial epithelial and inflammatory cells, while leptin expression was observed in alveolar cells and IL-6 expression in blood vessel cells only. Serum levels of leptin and IL-6 were significantly higher in COPD1 and COPD2 rats compared with the control rats, and were even higher in COPD1 rats than COPD2 rats. In conclusion, leptin and IL-6 levels were demonstrated to be associated with the severity of COPD.