This paper reports all experimental and computational thermochemical Study on 5,5-dimethylbarbituric acid and the solid-phase structure of the compound. The value of the standard (p degrees = 0, 1 MPa) molar enthalpy of formation in the gas phase at T = 298.15 K has been determined. The energy of combustion was measured by static bomb combustion calorimetry, and from the result obtained, the standard molar enthalpy of formation in the crystalline state at T = 298.15 K Was calculated as -(706.4 +/- 2.2) kJ.mol(-1). The enthalpy Of sublimation was determined using a transference (transpiration) method in a saturated NB, stream, and a Value of the enthalpy Of sublimation at T = 298.15 K was derived as (115.8 +/- 0.5) kJ.mol(-1). From these results a value of -(590.6 +/- 2.3) kJ.mol(-1) for the gas-phase enthalpy of formation at T = 298.15 K was determined. Theoretical C calculations at the G3 level were performed, and a Study on Molecular and electronic Structure of the compound has been carried Out. Calculated enthalpies of formation are in reasonable agreement with the experimental value. 5,5-Dimethylbarbituric acid was characterized by single crystal X-ray diffraction analysis. In the crystal structure, N-H center dot center dot center dot O=C hydrogen bonds lead to the Formation of ribbons connected further by weak C-H center dot center dot center dot O=C hydrogen bonds into a three-dimensional network. The molecular and supramolecular Structures observed in the solid state were also investigated in the gas phase by DFT calculations.