Simulation of pulmonary drug delivery systems is a very complex and challenging process. However, the use of predictive in silico models is always a valuable approach during drug formulation development. The current study was designed to investigate the impact of Calu-3 permeability on the in silico pharmacokinetic (PK) prediction of inhalation products. Formoterol was chosen as model API and its permeability on Calu-3 cells was measured in vitro. An in silico physiologically based pharmacokinetic (PBPK) model of formoterol from an inhaled formulation (Foster® pMDI) was firstly built using GastroplusTM (Simulation Plus, Inc.), based on in vitro physio-chemical characteristics, physiological input parameters and published in vivo lung deposition data. In order to assess the predictability of the current model without using in vivo lung deposition data, the software calculated lung deposition results based on formulations characteristics were utilized for the PK prediction in the second part of this study. The variation of predicted plasma profiles of marketed inhaled formulations containing formoterol (Foster®pMDI, Symbicort® pMDI and Foradil®DPI) were estimated and compared with in vivo plasma profiles obtained from published clinical data. As shown in this study, using in vitro Calu-3 permeability can help to build and to optimize the PBPK models of inhaled formoterol formulations.