Owing to the existence of simple equivalent circuits, the synthesis of transfer functions can be conveniently realized using symmetrical two-port networks. This is always possible exactly for transimpedance and transadmittance functions, and for less than a multiplicative constant in the case of voltage or current ratios. In this Letter, the canonical unbalanced realizations of symmetrical two port networks are derived using the eigendecomposition of the open circuit impedance matrix Z. This derivation is presented both in the frequency (phasor) domain and in the Laplace domain. The proposed approach can be of interest since it provides an alternative proof of well known equivalent circuits; moreover it gives an interpretation of such schemes in terms of eigenvalues and eigenvectors of impedance matrix. Finally, the extension of the proposed approach to reciprocal (nonsymmetric) two-port networks is discussed.