Several mathematical models have been developed to simulate the geometry of human lung airways. Commonly used models represent pre-specified geometries for human lung, such as diameter, length, number of airways, branching and gravity angles. Hofmann provided a set of statistical distributions for the above mentioned parameters of human lung structure by using more resin casting samples. Airflow and particle deposition in human lung have been analyzed by a number of researchers. Even though some of them have simulated deposition in a sample bifurcation, through a set of airways, or in a symmetric lung, but none of them have simulated a whole asymmetric, unpredefined lung yet.In this project particle deposition in the five lobes of human lung is simulated. The simulation is based on a stochastic lung model, derived from detailed morphometric measurements of Raabi and Hofmann. Pathways are simulated using Monte Carlo methods; consequently the whole lung structure changes both stochastically and statistically in each simulation. These stochastic lungs contain about 14 millions airways and 8 millions single paths.Acinar region is assumed as a pack connected to the last tracheobronchial tree airways. This pack contains 9 generation and has 0.187 cm 3 volume.In the previous works, flow division in bifurcations is started from trachea and is continued downward. Furthermore, whole long airways have not been simulated in these earlier works. As a result ducts outlet boundary conditions could not be determined accurately in these simulations. According to the physiology of respiratory system, air suction during iiration is caused by the volume change of the pulmonary airways. In this study flow rates in airways are computed in an upward manner starting from the acinus packs (where suction occurs), following to trachea. The flux distribution results are compared to the previous available assumptions, i.e., flow divisions according to the ratio of daughters’ cross sections. Regional and total deposition fractions in the human respiratory system are computed by the stochastic lung deposition model during inhalation, exhalation and breath hold periods. These fractions are computed in a stochastic lung instead of a pre-defined lung structure. Three case of inhalation are considered in this study: i. oral breathing, ii. nasal breathing and iii. trachea breathing. Simultaneous effects of Brownian motion, inertial impaction and gravitational sedimentation are simulated in particle deposition analysis in respiratory airways using analytical equations. The effects of particle size, density and inhalation flow rate variation are also analyzed in this study. Key words Monte Carlo modeling, Whole lung, Five lobes, Acinar pack, Flow division, Deposition fraction.