Background and purpose: Chronic Obstructive Pulmonary Disease (COPD) is a major cause of morbidity and mortality in India. It is characterized by dyspnoea and limited exercise capacity. It has been proved that breathing exercises spontaneously reduce dyspnoea and mechanical work of breathing in subjects with COPD, thus gaining an important part in pulmonary rehabilitation. The aim of this study was to determine the energy expenditure in people with COPD before and after performing three commonly used breathing exercises by using the Physiological Cost Index (PCI) as a tool. Study Design: Experimental pre test __ampersandsignndash;post test. Materials and Methods: The PCI of 30 male patients were studied on two occasions, before performing exercise and after performing two commonly used breathing exercise viz, Diaphragmatic Breathing (DB) and Pursed Lip breathing (PLB). Results: Following the breathing exercise the PCI decreased in 22 patients, in 6 patients it was unchanged and in 2 patients it was increased. The mean PCI value before breathing exercise was .3099(range .13 - .67) and that after breathing exercise was .2387(range .07 -.75). Conclusion: The Physiological Cost Index (PCI) of subjects suffering from Chronic Obstructive Pulmonary Disease (COPD) was seen to decrease after performing two commonly used breathing exercises, thus indicating a favourable decrease in energy expenditure following the breathing exercises.