Nutritional disorders in patients with chronic obstructive pulmonary disease (COPD) are associated with cachexia, sarcopenia, and weight loss. In particular, weight loss is a prognostic factor in COPD independent of pulmonary function, and energy malnutrition is a contributing factor. Frequent exacerbation hospitalization is also a prognostic factor for COPD patients. The impact of energy malnutrition on adverse events such as exacerbation hospitalization is unknown, and this study aimed to investigate that. We included 163 male subjects with COPD. Respiratory quotient (RQ), an index of energy malnutrition, was calculated by expiratory gas analysis using an indirect calorimeter. RQ <0.85 was categorized as the energy malnutrition group. Kaplan-Meier analysis was used to compare the hospitalization avoidance rate between the with and without energy malnutrition groups. Independent factors associated with exacerbation hospitalization were evaluated by Cox regression analysis. We finally analyzed data from 56 selected subjects (median age: 74 y). The exacerbation hospitalization rate was significantly higher in the energy malnutrition group. Fifty percent of the energy malnutrition group was hospitalized for an exacerbation, and the median hospitalization avoidance time was 701 d. In Cox regression analysis (adjusted for age, BMI, mMRC dyspnea scale score, %FEV₁, and 6-min walk test), energy malnutrition was an independent factor associated with exacerbation hospitalization (HR 4.14, 95% CI 1.13–15.1, p=0.03). Energy malnutrition may be the risk factor for exacerbation hospitalization. Energy malnutrition may be an early nutritional disorder and early detection and intervention may reduce exacerbation hospitalizations.