In this article, characteristic modes for metallic-dielectric composite structures (MDCS) are explored for fast and accurate analysis of scattering from large antenna arrays. Specifically, a generalized eigenvalue equation is formulated from a method of moments (MoM) impedance matrix of the electric field integral equation and Poggio, Miller, Chang, Harrington, Wu, and Tsai formulation. Modal currents for an antenna element with MDCS are then used as entire domain basis functions in the MoM for expanding equivalent currents over a large antenna array with MDCS. Only a small number of the modal currents are required to approximate the induced current over the antenna array with sufficient accuracy. Thus, the number of the unknowns and the corresponding CPU time in the MoM are significantly reduced in the proposed method. Furthermore, as the periodicity and intrinsic relationship of the matrix elements are considered when using the modal currents as entire domain basis functions, the computational efficiency of the proposed method is further improved. Numerical results of typical antenna arrays with MDCS are presented to illustrate the efficiency and accuracy of the proposed method.