Pulmonary toxicity of CNTs is well established by many laboratory investigations. The toxicity studies were challenging due to lack of occupational exposure assessments. In the present study exposure assessment of MWCNTs was carried out by measuring the mass concentrations in personal breathing zone of a manufacturing facility using filter sampling procedure. The measured concentrations were used to calculate the amount of MWCNTs that can be deposited on the alveoli of human lung. The obtained results indicate that the amount of CNTs that will be deposited on the pulmonary alveoli / day / body weight is 0.179μg/kg/day.