We report a method for estimating the effective molecular diffusivity of mixed matrix membranes (MMMs) with tubular tillers. This method is based on constructing three-dimensional MMM models for solving Pick's diffusion equation to obtain the concentration profiles. The effective diffusivity of the MMMs was thus derived from the concentration distributions. Using this approach, the effects of various structural parameters, including the tubular filler volume fraction, spatial distribution, orientation, aspect ratios, and diffusivity ratios, were assessed. The results suggest that the tubular filler alignment and spatial distributions are critical to the mass transfer in MMMs. We compared the diffusivity estimated by the presented method to the experimental data Our approach shows improved predictions compared with the Maxwell model and the Kang-jones-Nair (K1N) model. Overall, this work presents a useful tool for understanding and designing MMMs with tubular fillers. (C) 2015 Elsevier B.V. All rights reserved.