Abstract. This paper is concerned with the following periodic Hamiltonian elliptic systemAssuming the potential V is periodic and 0 lies in a gap of σ(−Δ + V ), G(x, η) is periodic in x and asymptotically quadratic in η = (ϕ, ψ), existence and multiplicity of solutions are obtained via variational approach.Mathematics Subject Classification. 35J50, 35J55.