A three-dimensional finite element analysis has been implemented to predict the transmission loss of an elliptic expansion chamber muffler for a given frequency range. Finite element models have been established by ANSYS 12.0.1. Results obtained from the model were compared with both experimental data obtained from previous work of Gerges et al. [1] . Comparison showed an excellent agreement between modeling results and experimental data. Six muffler configurations of different major/minor axis ratios of elliptic expansion chamber (a/b), with equal chamber volume have been modeled. Results demonstrated the ability of FEM to represent the acoustic attenuation performance of acoustical muffler. It also showed the effect of (a/b) ratio on the cut-off frequency due to multidimensional modes propagation. The FEM results were interpreted in various muffler configurations to determine the relationship between the number of domes in transmission loss characteristic curve and (a/b) ratio.