Objective: Chronic Obstructive Pulmonary Disease leads to dyspnea and fatigue by causing malnutrition and impaired respiratory muscle strength in patients. This study was conducted to determine the factors associated with body mass index, fatigue, and dyspnea levels in patients with Chronic Obstructive Pulmonary Disease. Method: This descriptive and relational study was conducted with 209 individuals in a clinic in Turkey. The data were collected using a questionnaire form, the Chronic Obstructive Pulmonary Disease, and Asthma Fatigue Scale, and the Dyspnea-12 Scale. In statistical analysis, standard deviation, independent group’s t-test, one-way analysis of variance, correlation analysis, and multiple regression analysis backward method were used. Results: Our data confirmed that fatigue and dyspnea are the major problems in Chronic Obstructive Pulmonary Disease patients, with a strong relationship between dyspnea and fatigue. In addition, a significant relationship was found between body mass index and fatigue and dyspnea scores. It was determined that individuals in the normal weight-underweight group had the highest fatigue and dyspnea mean scores. Besides, the multiple regression analysis showed that 46% of the variance in fatigue was explained by the predictive variables. Conclusions: It is important for healthcare professionals to evaluate patients according to their body mass indexes and to consider variables that affect fatigue and dyspnea. Due to the limited number of studies in the literature, it may be suggested to conduct more studies on this topic.