A three-dimensional, full-scale, single-phase finite element model has been developed for a liquid-fed direct methanol fuel cell (DMFC) with serpentine flow patterns. Equations for conservation of mass, momentum, and species are coupled with electrochemical kinetics in anode and cathode catalyst layers (CCLs). At the anode and cathode sides, only the liquid and the gas phases are considered, respectively. The significant benefit of a full-scale model is that the effect of physical parameters and distribution of the concentration of species can be realized in different channels for a desired section within the flow patterns. The model is used to study the effects of different operating parameters on fuel cell performance. Comparing numerical and experimental results demonstrate that the single-phase model slightly over-predicts the results for polarization plot. The modeling results also show that the porosity, temperature, and methanol concentration play a key role in affecting the DMFC polarization curve.