The method of substructure synthesis has been extended to systems with viscoelastic damping in hereditary integral form, differential operator form and steady-state form. Based on a variational principle for symmetric systems, the corresponding substructure synthesis method is formulated in the frequency domain. Each substructure is represented by a set of admissible trial vectors in the Rayleigh-Ritz method. Eigenvectors of the corresponding undamped substructure and Ritz vectors obtained by spatial discretization of admissible functions are recommended as trial vectors. The effectiveness of the proposed method in terms of reducing the size of final equations is illustrated through numerical examples.