The solubilities of betulin and betulinic acid were measured at varied values of mole fraction of sodium hydroxide aqueous solutions at a series of temperature (283.2, 293.2, 303.2, 313.2, and 323.2) K. They increase with the increase of temperature. Furthermore, the solubility of betulinic acid has a positive correlation with the mole fraction of sodium hydroxide aqueous solutions, and so is that of the betulin. The experimental solubility resuls are well correlated by the modified Apelblat equation. The enthalpy and entropy of betulin and betulinic acid during the dissolution process in sodium hydroxide aqueous solutions are calculated with the van't Hoff equation. The results indicate that the dissolution process is endothermal reaction that is driven by entropy. (c) 2013 Elsevier Ltd. All rights reserved.