The　dissociation　constant　(pK(a))　of　(S)-2-hydroxy-4-phenylbutyric　acid　((S)-HPBA)　was　determined　at　298.2　K　by　potentiometric　titration.　(S)-HPBA　exhibits　a　pK(a)　value　of　3.81.　The　solubility　of　(S)-HPBA　in　toluene　from　(288.2　to　343.2)　K,　in　water　from　(283.2　to　333.2)　K,　and　in　ethyl　acetate　from　(278.2　to　313.2)　K　was　measured　by　the　steady-state　method.　The　solubility　in　all　selected　solvents　increases　with　the　increase　of　temperature.　The　solubility　of　(S)-HPBA　in　ethyl　acetate　is　much　greater　than　that　in　water　or　toluene.　Water　was　found　to　be　a　fine　alternative　to　toluene　for　crystallizing　(S)-HPBA　and　ethyl　acetate　to　be　a　suitable　extraction　solvent　of　(S)-HPBA　in　the　pharmaceutical　industry.　The　experimental　solubility　data　were　correlated　with　the　modified　Apelblat,　Redlich-Kister,　Wilson,　and　universal　quasichemical　activity　coefficient　(UNIQUAC)　equations,　respectively.　The　Wilson,　Redlich-Kister,　and　modified　Apelblat　equations　show　better　agreement　with　the　experimental　solubility　data　of　(S)-HPBA　in　toluene,　water,　and　ethyl　acetate,　respectively.　The　solubility　of　(S)-HPBA　in　aqueous　solutions　over　the　pH　range　from　1.48　to　5.45　at　298.2　K　was　also　determined　by　the　steady-state　method,　and　the　corresponding　solubility　data　were　separately　fitted　well　with　a　semi-Henderson-Hasselbalch　equation　(pH　＜=　4.0)　and　a　linear　equation　(pH　＞　4.0).