Isothermal-isobaric Monte Carlo (NPT-MC) simulations and the Widom test particle method were used to predict the solubility of the explosive 1,3,5-trinitro- 1,3,5-s-triazine (RDX) in supercritical CO2. A Lennard-Jones potential energy function was chosen to describe the interaction between RDX and CO2, and calibrated using two experimental solubility values. NPT-MC simulations using this interaction potential predicted solubilities of RDX in CO2 over a temperature range of 308 to 353 K and pressures ranging from 10.4 to 48.3 MPa that were in good agreement with experimental values.