The widespread research of ionic liquids is mainly because of their unique characteristics, which allow the possibility for more efficient reactions and separations in chemical processes. To achieve a successful commercial status, several problems of ionic liquids should be solved, including loss of ionic liquids and high viscosity that effects on fluid flow and mass transfer. In this study, hollow polysulfone microcapsules filled with ionic liquid of 1-butyl-3-methylimidazolium hexafluorophosphate [BMIM]PF6 were prepared via a two-stage microfluidic approach. The results of the preparation showed that [BMIM]PF6 was Successfully encapsulated with polysulfone, as an encapsulation capacity of 30.8% was achieved. Smaller microcapsules were produced with smaller size of nozzle, lower droplet phase flow rate or higher continuous phase flow rate. The microcapsules had excellent monodispersity and spherical morphology with extremely narrow size distribution. Besides, they had good stability of ionic liquid immobilization. The microfluidic approach has been proved successful to fabricate microcapsules, with advantages of extremely narrow size distribution, easy-controlled operating conditions to obtain different size of microcapsules, possibility for on line observation of preparation process. (c) 2006 Elsevier B.V. All rights reserved.