The present study investigates the polydisperse particle deposition in an idealized mouth-throat. The scope is the identification of the properties of polydisperse particle deposition in the human upper airways with respect to the aerosol drug delivery to the lung. Both one-way and two-way coupling between the gas and the particle phases are implemented to model the two-phase flow. Large eddy simulation (LES) with the Smagorinsky subgrid model is used to simulate the laminartransitional-turbulent gas flow, and the model is combined with Lagrangian equations to describe the particle motion. User-defined solvers based on the open-source software OpenFOAM are developed to solve the governing equations. An experimental particle size distribution from a dry powder inhaler with 200 mu g dosage corresponding to one actuation is used. The numerical results show that the polydisperse particle deposition in the human mouth-throat is dominated by the particle size distribution and the geometric characteristics of the idealized mouth-throat. Moreover, simulations with two different monodisperse aerosols with different particle sizes are used for comparison: the representative Sauter mean diameter and the mass median diameter of the reference polydisperse particle size distribution. The particle deposition efficiency of the polydisperse particle distribution is much higher than that of both monodisperse particle distributions, which cannot represent the polydisperse particle deposition characteristics. The particle deposition efficiency is higher using one-way coupling compared to two-way coupling for the polydisperse particle size distribution. It is concluded that a representative polydisperse particle distribution should be used to simulate the aerosol drug deposition in the human respiratory system using two-way coupling.