Chronic obstructive pulmonary disease (COPD) is an inflammatory lung disease characterized by inflammatory cell activation and the release of inflammatory mediators. Interleukin-33 (IL-33) plays a critical role in various inflammatory and immunological pathologies, but evidence for its role in COPD is lacking. This study aimed to investigate the expression of IL-33 in COPD and to determine whether IL-33 participates in the initiation and progression of COPD. Levels of serum IL-33 and its receptors were measured by ELISA, and serum levels of IL-33, ST2, and IL-1 receptor accessory protein were elevated in patients with COPD compared with control subjects. Flow cytometry analysis further demonstrated an increase in peripheral blood lymphocytes (PBLs) expressing IL-33 in patients with COPD. Immunofluorescence analysis revealed that the main cellular source of IL-33 in lung tissue was human bronchial epithelial cells (HBEs). Cigarette smoke extract and lipopolysaccharide could enhance the ability of PBLs and HBEs to express IL-33. Furthermore, PBLs from patients with COPD showed greater IL-33 release in response to the stimulus. Collectively, these findings suggest that IL-33 expression levels are increased in COPD and related to airway and systemic inflammation. Therefore, IL-33 might contribute to the pathogenesis and progression of this disease.