This study reports computational fluid dynamics simulation of gravitational settling effects on inhaled submicron bioaerosol particle deposition in the human lung airway. The study focused on trachea and main bronchus (tracheobronchial) sections, the upper anatomical unit of lung’s respiratory tract. A commercial finite-volume code, ANSYS Fluent, enhanced with user-supplied programs in Visual C++, has been employed. Tracheobronchial (TB) geometry was developed using ANSYS Design-Modeler and the dimensions were based on widely used human lung’s morphological dimensions specified in Ewald R. Weibel’s model of dichotomous lung morphometry. Simulation results were compared with Pich’s mathematical model for inhaled bioaerosol particles’ sedimentation deposition. Although, the inertial impaction is still a dominant deposition for submicron particle in the TB airways under light physical activity of breathing condition (Qin = 28.3 L/min), the gravitational settling (GS) may play a role as well. Study results revealed the GS is negligible for smaller particle (size < 1 μm), whereas, it becomes dominant for larger particles (size > 1 μm). The GS has 15 times stronger deposition effects on a 10 micron particle than that of a 1 micron particle. Both the model result and previously reported literature supported this statement. The occurrence of inertial impaction causing the location of deposition “hot spots” in the bifurcating airway where sharp bends exist is also discussed.