A new class of materials, melaminate salts of potassium and rubidium, has been obtained by deprotonating molecular melamine in liquid ammonia. Potassium melaminate KC3N6H5·NH3 and rubidium melaminate RbC3N6H5·1/2NH3 were characterized by single-crystal XRD, showing that the melaminate anion is slightly distorted compared to the neutral molecule due to the ionic imine group, but it still forms extensive hydrogen bonding networks. The melaminate anion also displays an increased coordination ability of μ4 and μ6+1 (the maximum for melamine is μ3). Thermal gravimetry coupled with mass spectrometry evidence a multistep decomposition with liberation of ammonia first and then cyanamide and larger fragments. A plausible decomposition mechanism is proposed. The infrared spectrum allows to identify the fingerprint of the melaminate vibrations such as to partially characterize the also synthesized amorphous sodium melaminate NaC3N6H5·nNH3 and the proposed tripotassium melaminate K3C3N6H3.