Ionic liquid-DMSO co-solvent system (20∶80 w/w) for recrystallizing RDX was investigated at 70 ℃. A non-agitated cooling crystallization method was employed for RDX growth and main collection, and rest RDX were collected by added some water or methanol to the filtrates. All the RDX samples were investigated by the DSC thermograph and SEM. The results obtained by the DSC thermograph and SEM show the thermal stability, purity, shape and quality of recrystallized RDX by Ionic liquid -DMSO co-solvent systems are improved while the H₂O-precipitated or the MeOH-precipitated materials are not. The recrystallized RDX in the DMSO-C₆mimBr co-solvent system are better than others.