Abstract: In recent years, eosinophil (EOS) has attracted much attention in the treatment of chronic obstructive pulmonary disease (COPD). Some COPD patients are observed with active airway inflammation and systemic inflammation, increase of circulating EOS, and a variety of involved inflammatory markers. At present, the relationship between EOS threshold and clinical treatment of COPD is still controversial, but EOS count has been used as a biomarker in clinical practice, especially in COPD patients gaining benefits of improving the prognosis and preventing the deterioration of the disease after inhaling corticosteroids. In addition, a variety of treatment methods for eosinophilic inflammation have been or are being researched and developed, including monoclonal antibodies against inflammatory mediators such as interleukin, chemokines and their receptors. This paper reviewed the biological characteristics of EOS, its role in the pathogenesis of COPD and its value as a biomarker in decision-making of individualized treatment.