Mixed matrix membranes (MMMs) are composed of a polymeric matrix, which gives them good processability, and crystalline microporous fillers, which give them high separation performance. The need to predict the separation performance of MMMs has led to the development of a number of analytical and numerical methods for the estimation of diffusivity in MMMs, based on the intrinsic diffusivity of the matrix and filler phases. However, current reports on the estimations of diffusivity in MMMs are only for flat dense MMMs (FDMMMs), rather than hollow fiber MMMs (HFMMMs), a scalable membrane configuration used in industrial membrane separation applications. In this paper, we presented the first numerical method for the estimation of effective diffusivity in HFMMMs. We determined that the curved geometry of HFMMMs results in mass transport pathways different from those found in FDMMMs, which produces higher effective diffusivity. We also investigated how the diffusivity and size of the filler as well as the interior diameter and thickness of the selective skin layer of HFMMMs affect diffusivity. The proposed methodology provides an effective tool for the design of high-performance HFMMMs applicable to cases involving separation. (C) 2015 Elsevier B.V. All rights reserved.