The problem of robust stability of discrete interval 2-D systems described by the second Fornaini-Machesini model is studied. By introducing interval uncertainty, a mathematical model of discrete interval 2-D systems is established. According to a kind of Lyapunov inequality criterion of 2-D systems and a positive definite lemma of a symmetric interval matrix, a sufficient condition for robust stability of the discrete interval 2-D systems is given. A numerical example shows the effectiveness of the sufficient condition for the robust stability of the 2-D systems.