Inclusion entrapped inside the crystals prepared in the cooling crystallization of cyclotrimethylenetrinitramine (RDX) from solution was Studied. Effect of supersaturation on the inclusion formation was also studied in crystallization using solvents. Solvents such as acetone (AC), cyclohexanone (CH), dimethylsulfoxide (DMSO), N-methylpyrrolidone (NMP), gamma-butyrolactone (BL), and their mixtures with water were investigated. The quantitative amount of inclusions entrapped in the RDX crystallized in various solvents was related to the supersaturation. The inclusion fraction in the crystals was affected by the supersaturation and the solvent. In order to decrease the inclusion fraction, ill the low supersaturation, AC and CH were recommended, while in high supersaturation, NMP and DMSO were desirable. Eventually the solvent effect on the inclusion was grasped by considering the supersaturation effect.