Energetic nitrate compounds, monomethylhydrazinium nitrate (MMH•HNO3) and monomethylhydrazinium dinitrate (MMH•2HNO3), were synthesized from hypergolic pair monomethylhydrazine (MMH) and nitric acid by mixing their diluted aqueous solutions carefully with an MMH:HNO3 molar ratio of 1:1 and 1:2, respectively. The overall ignition and combustion behaviors of these two nitrate-based monopropellants were examined by using a high-pressure strand burner with optical access, coupled with a high-speed video camera for capturing and analyzing the condensed- and gas-phase processes as well as measuring the regression rates of the solid strands. MMH•2HNO3, which has a stoichiometric F/O ratio, has a burn rate of 0.56 mm/s in 1 atm of N2. Its burn rate increases almost linearly with pressure up to 800 psi at which the burn rate is about 14 mm/s. However, the burn rate of MMH•2HNO3 increases sharply to about 400 mm/s at 1000 psi. MMH•HNO3, which is a fuel-rich compound and highly hygroscopic, is very difficult to ignite. Thermal decomposition of a small amount (~1.5 mg) of MMH•2HNO3 and MMH•HNO3 was investigated by a confined rapid thermolysis setup with heating rates on the order of 2,000 K/s coupled to rapid-scan Fourier transform infrared (FTIR) spectroscopy of the evolved gases. Both MMH•2HNO3 and MMH•HNO3 start to decompose rapidly at around 120°C, and the important IR-active species evolved from the decomposition of these salts include HNO3, CH3ONO2, CH3N3, HN3, H2O, N2O, NO, NO2, CH4 and CO2. Possible decomposition pathways are also discussed based on the rapid thermolysis studies.