The equilibrium solubility of N-(9-fluorenylmethoxycarbonyloxy)succinimide in {dimethyl sulfoxide (DMSO), ethanol, ethylene glycol (EG), N,N-dimethylformamide (DMF)} plus water were determined by means of the isothermal equilibrium method at (283.15328.15) K under atmosphere pressure. The measured values of N-(9-fluorenylmethoxycarbonyloxy)succinimide are positively increased with the increase of temperature in a certain cosolvent composition; however, that decreased when the content of water was gradually increasing and the largest solubility data was observed in pure DMF (0.04989 in mole fraction, 328.15 K). The mole fraction solubility in monosolvents ranked as DMF (9.693 X 10(3), 298.15 K) > DMSO (6.406 X 10(3), 298.15 K) > ethanol (8.237 X 10(4), 298.15 K) > EG (3.136 X 10(4), 298.15 K) > water (7.378 X 10(6)). Under conditions of the same temperature and cosolvent composition, the solubility maximum of N-(9-fluorenylmethoxycarbonyloxy)succinimide was found in (DMF + water, 9.693 X 10(3) in mole fraction in DMF, 298.15K) than in the other aqueous mixtures system. The solid phase crystal samples of N-(9-fluorenylmethoxycarbonyloxy)succinimide were detected by XPRD which indicated clearly that there is no polymorphic transformation, solvate formation, or crystal transition for crystallized samples. General cosolvency models such as the JouybanAcree model, vant HoffJouybanAcree model, and ApelblatJouybanAcree model served to calculate and correlate the obtained solubility. Consequently, the difference between the measured values and calculated ones was quite small at evaluated temperatures so as the highest RAD ((X)10(2)) and RMSD ((X)10(4)) were 2.95 and 3.24, respectively.