Nabumetone, non-steroidal anti-inflammatory drug, is a poorly water-soluble drug and has low bioavailability on oral administration. One of the important methods to improve the solubility and bioavailability of a less water-soluble drug is by the use of cosolvents. The solubility enhancement produced by binary blends with a cosolvent (dioxane) was studied against the solubility parameter of solvent blends (δ1) to evaluate the solubility parameter of drug (δ2). Solubility parameter of drug (δ2) was evaluated in blends of dioxane-water system. The results obtained were compared with the δ2 values obtained using Molar Volume Method and Fedor’s Group Substitution Method. The binary blend water-dioxane (10:90) gave maximum solubility with an experimental δ2 value of 11.354 (Cal/cm3)0.5 that was comparable to the theoretical values of 11.354 (Cal/cm3)0.5 determined by Molar Volume Method and 10.1689 (Cal/cm3)0.5 when determined by Fedor’s Group Substitution Method, which is still in good agreement with solubility measurement method.