To enhance the solubility of poorly water-soluble ibuprofen with poloxamer and menthol, the effects of menthol and poloxamer 188 on the aqueous solubility of ibuprofen were investigated. In the absence and presence of additives such as ethanol and poloxamer 188, the solubility of ibuprofen increased until the ratio of menthol to ibuprofen increased from 0:10 to 4:6 followed by an abrupt decrease in solubility above the ratio of 4:6, indicating that 4 parts of ibuprofen formed eutetic mixture with 6 parts of menthol. In the presence of poloxamer, the solutions with the same ratio showed abrupt increase in the solubility of ibuprofen. Furthermore, in the presence of poloxamer, the solution with ratio of 4:6 showed more than 2.5- and 6-fold increase in the solubility of ibuprofen compared with that without additives and that without menthol, respectively. The solution with menthol/ibuprofen ratio of 1:9 and higher than 15% poloxamer 188 showed the maximum solubility of ibuprofen, 1.2 mg/ml. Thus, menthol gave the greatly enhanced solubility of ibuprofen with poloxamer 188.