In the title salt, C5H8N3 (+)·C3H3O4 (-), the 3,4-di-amino-pyridinium cation is almost planar, with an r.m.s. deviation of 0.02 Å. The conformation of the hydrogen malonate anion is stabilized by an intra-molecular O-H⋯O hydrogen bond, which generates an S(6) ring. In the crystal, N-H⋯O hydrogen bonds link cations and anions into layers parallel to the ab plane.