Lattice Boltzmann (LB) methods are employed to simulate the structural evolution of asymmetric membranes during the immersion precipitation fabrication process. A multi-phase, multi-component LB model is first developed, based on forcing interactions of the Flory-Huggins type. Boundary conditions specific to the process of immersion precipitation are then applied. Results of the time-dependent, two-dimensional simulation qualitatively capture major characteristics of asymmetric membrane formation such as membrane compaction and formation of a selective skin layer. Simulated effects of viscosity and forcing interactions on the final membrane structure agree qualitatively with experimental reports, suggesting the potential application of LB methods to process design for optimizing membrane morphology and performance. (C) 2004 Elsevier B.V. All rights reserved.