This study obtained the most penetrating particle size of dust-loaded fiber filters for polydispersed aerosol. The enhancement factor (lambda) introduced by Kanaoka et al. [4] was generalized for different interception parameter and by using the simplified generalized formula, the most penetrating particle size and minimum collection efficiency for dust loaded filters was estimated. The most penetrating particle size decreases as flow velocity increases, which means that the most penetrating particle size shifts to a smaller size as flow velocity increases. This tendency is stronger for filters with dust-loaded particles than for clean filters. In addition, the results showed that the minimum collection efficiency increases as dust loading increases. The increased enhancement factor increases the interception parameter and reduces the most penetrating particle size. Further, this study calculated the most penetrating particle size of dust-loaded fiber filters by using the generalized enhancement factor obtained under the assumption of the linear approximation of the coefficient regarding the interception parameter. (c) 2013 Elsevier B.V. All rights reserved.