In this research, thermal of level comfort and air quality indoor were examined for different numbers of persons (occupants’ density) within a (3m × 2.5m × 2.5 m) office room. The office room is equipped with mixing ventilation system, temperature and air speed (17°C) and (2.5 m/s) respectively. The results of experimental experiments and results were compared with computational fluid-dynamics (CFD) analysis utilizing the turbulent (RNG, k-epsilon) model on a thermal manikin that represents a person’s body in a standing and sitting and position. The experimental study focused on measuring the velocity, air temperature, and carbon dioxide (CO2) concentration in different areas indoor the room, in addition to taking measurements around the heat manikins and in the breathing area. When analyzing numerical data, thermal of level comfort was assessed by air diffusion of performance Index (ADPI), predicted of percentage dissatisfied (PPD), and predicted of mean vote (PMV). The results indicate that thermal comfort and indoor air quality decline with more persons. Where the values of (ADPI), (PPD) and (PMV) change from (76.55 %), (6.325 %) and (0.021) to (64.25 %), (10.412 %) and (0.52) respectively, when the number of persons in the room increased from (two persons) to (four persons).