Anomaly of a discrete symmetry is defined as the Jacobian of the path-integral measure. Assuming that anomaly at low energy is cancelled by the Green–Schwarz (GS) mechanism at a fundamental scale, we investigate possible Kac–Moody levels for anomalous discrete family symmetries. As the first example we consider discrete abelian Baryon number and Lepton number symmetries in the minimal supersymmetric standard model with see-saw mechanism, and find that the ordinary unification of gauge couplings is not consistent with the GS conditions, indicating a possible existence of further Higgs doublets. Next we consider the recently proposed supersymmetric model with Q6 family symmetry. In this model, the GS conditions are such that the gauge coupling unification appears close to the Planck scale.