Resumen: Introduction: Obesity and breast cancer (BC) are two diseases with known symptoms; however, the association of both and its impact on the respiratory system is poorly investigated. Objective: To describe the effects of overweight and obesity on the pulmonary volumes of patients with breast cancer from the city of Talca. Method: Forty-one women diagnosed with BC were divided into three groups: Nine patients with breast cancer and normal weight (BC + NW), 18 with breast cancer and overweight (BC + OW) and 14 with breast cancer and obesity (BC + O). Forced vital capacity and lung volumes were measured, ANOVA or Kruskal-Wallis was used for the statistical analysis, and for the Pearson or Spearman correlations, a level of significance of p < 0.05 was considered. Results: Patients with BC + NW had a greater residual volume than those with BC + OW and BC + O (both p < 0.05). Functional residual capacity (FRC) was significantly higher in patients with BC + NP versus patients with BC + OW and BC + O (both p < 0.05). The total lung capacity was significantly higher in patients with BC + NW versus BC + OW and BC + O (p < 0.01 and p < 0.001, respectively). Between the BMI and FRC, a negative and significant correlation was found in the patients with BC + O (p = 0.049). Finally, in patients with BC + O a positive and significant correlation was observed between height and FRC (p = 0.01). Conclusions: The decrease in pulmonary volumes is exacerbated when patients with BC present malnutrition by excess. In addition, it is negatively correlated with the BMI in patients with BC + O.