The solubilities of forms I and II of clopidogrel hydrogen sulfate (CHS) in methanol + 2-propanol mixture were measured over the temperature range of (-5 to +55) degrees C and the methanol mass fraction range of (1.0 to 0.1). Enthalpy and entropy of dissolution of forms I and II of CHS in methanol +2-propanol were determined by using the van't Hoff equation. Form II had a lower solubility and a higher enthalpy of dissolution compared to those of form I, which indicated that form II was the stable form and form I was the metastable form at the studied temperature range of (-5 to +55) degrees C.