This study presents the results of a series of numerical simulations for airflow field and particle dispersion and deposition around a mannequin standing inside a ventilated room. A 3-D airway model was constructed from the nostril inlet to the end of 4th lung generation and was integrated into the standing mannequin model in the room. The computational domain included the region around the mannequin and inside the respiratory system. The room was ventilated by a mixing air-conditioning system that supplied air with a speed of 3m/s from a diffuser mounted on the top of the sidewall and exited from a damper mounted at the bottom of the side or front walls. In the first mode, the diffuser and damper were located on the wall in front of the mannequin and in the second mode on the wall at the right side of the mannequin. The mean airflow field inside the room was obtained by solving the Navier-Stokes and continuity equations using the Ansys-Fluent software. The k-ω SST transitional model was employed for turbulence modeling. Then, spherical particles with 5, 10, 20, and 40 μm diameter and unit density were released into the room, and their trajectories were tracked by using the Lagrangian trajectory analysis approach. Aspiration efficiency and deposition of particles for inhalation flow rates of 15 and 30 lit/min were analyzed with the improved discrete random walk (DRW) stochastic model using a user-defined function (UDF) coupled into the Ansys-Fluent discrete phase model. Simulation results for the mean airflow showed the formation of a large recirculation zone inside the room. In the first mode, the main recirculation zone formed behind mannequin that carried the flow streamlines toward the mannequin breathing zone. In the second mode, the recirculation formed in front of the mannequin face that led the streamlines out of the breathing zone. The simulation results for particle inhalation showed that the aspiration efficiency of particles is higher in the first ventilation mode compared to the second mode. Results also showed that the total deposition of particles in the airway passage increases as particle size increases.