Clinical investigation shows a dramatic relation between deposition of particles in lung's pathways and respiratory system diseases. Particle deposition may also play a major role in drug delivery via respiratory system. Previous researches on symmetric and 5-lobe models for rat, dog, hamster and human show that, the deposition fraction of fine particles (between 0.1 and 0.7 mu m) is minimum. A multi-path asymmetric 5-lobe model of Horsfield et al. is employed to construct the airway tree. Since the data are based on lung casting, asymmetric properties of the model are more realistic. Deposition of 0.01-10 mu m particles is calculated during inhalation using published formulas in every branch. Here, we measured the deposition up to alveolar region. Accumulative deposition versus particle diameter predicts less deposition in comparison with symmetric models in as much as our model is asymmetric. The flow is divided based on distal volume. Particle deposition for 0.01 mu m is in good agreement with other models but for 1 gm different trend in lower generations is observed. It is concluded that the asymmetric pattern gives different deposition fraction in all regions, since the distinctive geometric properties of the model is in some extent different from that of symmetric model. But, the accumulative deposition trend is similar in both symmetric and asymmetric models. (C) 2010 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.