Hydroxylammonium nitrate (HAN)-based monopropellants are among the most promising candidates for eco-friendly rocket engine propellants. They are not carcinogenic or mutagenic, and their thermal decomposition reactions are sufficiently exothermic for military and aerospace applications. Here, an experimental analysis was performed to investigate the characteristics of HAN-based mixtures for monopropellant applications. Three kinds of propellants were prepared for this study: a HAN-water solution, a HAN-water solution with methanol added at a stoichiometric ratio, and a third solution where water was added to further dilute the solution. Two different experimental techniques were used under atmospheric pressure of nitrogen gas environment: thermal analysis and droplet evaporation analysis. Thermal and catalytic decomposition were analyzed using thermo gravimetric analysis. Droplet evaporation was analyzed using a cylindrical vessel equipped with a heating system and a droplet feed, and a high-speed charge-coupled device (CCD) camera. These data were post-processed to calculate the temporal variation of the droplet diameters.