A mathematical model for alkaline fuel cell cathodes was developed by using concentrated solution transport theory to simulate and study the electrode operation. The model assumed an electrode with two layers: gas-supply layer and reaction-active catalyst layer. The processes considered in the model include: Multiple component gas diffusion in both the gas-supply and catalyst layers, multicomponent transport in the concentrated electrolyte of the catalyst layer, phase equilibrium of water in the gas and liquid phases of the catalyst layer, reactant gas transport both in the electrolyte film and agglomerates within the catalyst layer, the electrochemical reaction of oxygen on the catalyst, and electronic conduction within the solid phase of the catalyst layer. The emphasis of the model simulation was given to study the effect of humidity content in the inlet reactant gas, electrode operating current density, and electrode operating temperature on the details of the electrode operation. The details considered comprise water flux transport in gas and liquid phase, both reaction and electrolyte concentration distributions inside the electrode, and electrode output potential. The results give interesting aspects of the water movement in the catalyst layer with important implications for the water balance of the electrode. Application of this model should be especially beneficial to the understanding of humidity content management during electrode operation.