The thermal decomposition of borazane BH3NH3 in the temperature range up to 500 K has been studied by differential scanning calorimetry (DSC) and thermogravimetry (TG) combined with the FTIR spectroscopic and mass spectrometric analysis of the gas phase. Above 340 K borazane is decomposed in stages as the temperature is increased. The exothermic decomposition is accompanied by the release of approximately 2.2 mol H-2/mol BH3NH3. This corresponds to a remarkable hydrogen storage density of 14.3 mass% related to the mass of borazane. In the gas phase above the solid decomposition residue monomeric aminoborane (BH2NH2), borazine (BHNH)(3), which is the boron-nitrogen analog of benzene, and traces of diborane B2H6 were found beside hydrogen. The release of significant quantities of borazine was observed only at temperatures above 400 K.