A phosphorus-containing name retardant (2,5-dihydroxyphenyl)diphenyl phosphine oxide (HPO) was characterized by a differential scanning calorimeter (DSC), thermogravimetric analysis (TGA), elemental analysis. and nuclear magnetic resonance ((1)H NMR and (31)P NMR) Using a static analytical method, the solubilities of HPO were measured in 12 solvents and correlated with an empirical equation. The estimated uncertainty of all of the solubility values on error analysis and repeated observations was within 2 0 %