Joint results of the differential scanning calorimetry (DSC) and thermogravimetry (TG) experiments were the basis for the fusion enthalpy and temperature determination of the biuret (NH2CO)2NH (synthesis byproduct of the urea fertilizer (NH2)2CO). Recommended values are DmH = (26.1 ± 0.5) kJ mol-1, Tm = (473.8 ± 0.4) K. The DSC method allowed for the phase diagrams of ‘‘water–biuret,’’ ‘‘water–urea,’’ ‘‘urea–biuret’’ binary systems to be studied; as a result, liquidus and solidus curves were precisely defined. Stoichiometry and decomposition temperature of the biuret hydrate identified, composition of the compound in ‘‘urea–biuret’’ system was suggested.