The dispersion relation for surface polaritons at the interface of two artificial composite media with time dispersion of permittivity Ε(ω) and permeability μ(ω) is derived. The system under study may exhibit properties of a 'left-handed' medium at microwave frequencies. It is shown that, depending on the sign of function Ε(ω), surface polaritons may be either forward or backward ones, and the number of branches in the spectrum of surface polaritons depends on the effective plasma frequency.