The solubility of the high-explosive cyclotrimethylenetrinitramine (RDX) in carbon dioxide (CO2) is measured over a temperature and pressure range of 303 K to 353 K and 6.9 MPa to 48.3 MPa, respectively. A high-pressure ultraviolet chromatographic detector is used to measure in situ solute levels of RDX in a dynamic flow apparatus. RDX is found to be relatively insoluble in CO2, with a maximum solubility of about 0.25 mg/g CO2 at the highest temperatures and pressures studied. Empirical fits of the solubility isotherms are determined as a function of the solvent density and solute vapor pressure. The spectroscopy of RDX is also examined as a function of CO2 temperature and pressure to confirm the suitability of the method for determination of solubility.