AbstractBackground: Smoking of cigarette remains the leading cause of preventable premature morbidity and mortality in both developed and developing countries. It is responsible for Coronary heart disease, 90% of chronic obstructive pulmonary diseases and lung cancer. The study is undertaken to highlight the critical effect of smoking. Objectives: 1. Effect of cigarette smoking on Hematological parameters and study them concerning the duration of smoking. 2. To study the Pulmonary function tests to detect emergency lung conditions in smokers with relation to duration and number of cigarettes smoked per day. Methods: A total of 100 healthy subjects (50 smokers) of age group 30-50 years were selected attending the out-patient department of KIMS. The control group (50 non-smokers) subjects were the non-teaching staff of KIMS Medical College. Hematological parameters such as Hb concentration, RBC count, TLC and Platelet count were performed using Hemo auto analyser Sysmex KX-21 and ESR was obtained by Westergren's method. Spirometry was performed using AD instrument. Results: Smoking caused abnormal Hematological parameters, which resulted in increased levels of Hb, RBC count, TLC, Platelet and ESR. (P<0.0001) And it had a negative impact on lung functions when compared to non-smokers. Smokers showed a significantly higher decline in PEFR, FVC, FEV1 and ratio of FEV1/FVC(P<0.001). Conclusion: Results showed abnormal hematological and pulmonary function tests which causes dangerous deterioration of lungs and human body function.