The performance of a hollow-fiber membrane contactor in removing ammonia from aqueous solution was simulated. An unsteady state 2D mathematical model was developed to study the ammonia stripping in the hollow-fiber membrane contactor. Two sets of equations were considered for the membrane contactor and the feed tank. CFD technique was applied to solve the model equations in which concentration distribution was determined using continuity equation. Velocity field is also determined using Navier-Stokes equations for the contactor. The model was implemented in linked MATLAB-COMSOL Multiphysics. COMSOL software was applied to solve the model equations for the contactor while MATLAB software was employed to consider changes in the concentration of the feed tank. Predictions of the model were then validated against experimental data which were found to be in good agreement. The assumption of Knudsen diffusion for the transport of ammonia molecules through the membrane pores increased the accuracy of the model. The effect of different parameters including feed velocity, feed concentration and pH on the removal of ammonia was investigated. The results of simulation revealed that the developed model can be used to evaluate the effective parameters which involve in the ammonia removal by means of membrane contactors. (C) 2011 Elsevier B.V. All rights reserved.