Chronic obstructive pulmonary disease(COPD) is currently the 4th leading cause of death all over the world. Smoking is by far the most important documented and preventable cause for COPD. We performed this study to identify the correlation of haematocrit and smoking score in pack years with severity of COPD. The study included 111 spirometry-confirmed COPD patients defined by the GOLD criteria from a tertiary care hospital in south India. They underwent detailed medical history and dyspnoea grading . Smoking status of the patient was noted and the severity of COPD was assessed according to GOLD classifications. All selected patients were subjected to blood investigations, chest Xray and ECG. 111 COPD patients were included in this study with mean of 57.48 ± 5.93 years. Among the study group large percentage of smokers(70.3%) used beedi. Polycythemia was detected in 97% of patients. Smoking in pack years also showed a close and significant relation to severity of COPD. Correlation between polycythemia with smoking score analyzed and pearson chi-square value is 35.5. Haematocrit of all a patients has gone above normal and was very high in heavy smokers. Fall in FEV1 was directly proportional to the pack years. Oxygen saturation of the smokers had a dramatic decrease with p value 0.019. There were significant correlation of smoking pack years with severity of airflow obstruction and oxygen desaturation . The onset of symptoms of COPD and the risk for polycythemia were also related to pack years.