Background: Breast cancer is the leading type of cancer among women globally, significantly impacting mortality and morbidity rates. Respiratory complications and diminished quality of life are common among patients undergoing chemotherapy, highlighting the need for effective supportive treatments. Objective: This study aimed to evaluate the efficacy of respiratory physiotherapy interventions, specifically breathing exercises, in improving lung function and quality of life in breast cancer patients undergoing chemotherapy. Methods: This quasi-experimental study enrolled thirty female breast cancer patients from the oncology wards of Allied Hospital and PINUM, Faisalabad. Participants were selected using a purposive sampling technique and were provided with respiratory physiotherapy, including spirometry and breathing exercises, three times a week for six months. Data were collected through initial and final assessments of lung function and quality of life, using self-administered questionnaires and spirometry. Ethical considerations followed the Declaration of Helsinki guidelines, with all participants providing informed consent. Statistical analysis was conducted using SPSS Version 25, employing the Wilcoxon signed-rank test. Results: The interventions showed statistically significant improvements in lung capacity; Forced Vital Capacity (FVC) and Forced Expiratory Volume in 1 second (FEV1) witnessed positive ranks in 22 and 21 patients respectively, with mean ranks of 11.50 and 11.00, and sum of ranks at 253.00 and 231.00 (p<.001 for both). Quality of life assessments indicated improvements across physical, emotional, and cognitive functions with significant p-values (<.001 to .025). About 70% of participants reported a good perception, and 10% reported an excellent perception of the physiotherapy's effectiveness in improving their condition. Conclusion: The study confirms that structured respiratory physiotherapy significantly enhances lung function and quality of life in breast cancer patients undergoing chemotherapy. These findings advocate for the integration of tailored respiratory physiotherapy into standard care protocols to improve clinical outcomes for this patient group. Keywords: Breast Cancer, Chemotherapy, Respiratory Physiotherapy, Breathing Exercises, Lung Function, Quality of Life, Patient Perception, SPSS Analysis, Oncology Rehabilitation.