Abstract : Asimple, accurate and controlled spectrophotometricmmethod is studied for the determinationmof hydroxychloroquine (HCQ) both pure and in pharmaceutical preparations. The drug's reaction with the 2,4-dinitrophenylhydrazine (2,4-DNPHz) reagent is the foundation of this mathod. The optimum conditions were studied from the effect of the reagent, oxidized agent and NaOH, the reaction time and the optimum temperature for the formation of the color of azo product and it was in compliance with Beer’s law in the range 2.5 to 22.5 µg/mL at the wavelength 620 nm. the molar absorptivity, Sandellʼs sensitivity, detection limit and quantitation limit were 1048.28L.mol-1 .cm-1, 0.3204μg.cm-2, 0.243 μg.ml-1,, and 0.738 μg.ml-1 respectively. The proposed method has been successfully applied to determination of HCQ in its pharmaceutical preparations. The thermodynamic functions such as enthalpy ∆H, entropy ∆S, and Gibbsmfree energy ∆G were calculated, and it was found that the drug absorption not Spontaneous,mendothermic process and more regular of the system.