The solubilities of sesquihydrous irbesartan hydrobromide in ethanol-water mixtures at pH 1.20 between (288 and 333) K are measured by the light extinction method. A laser technique that determines the mass of suspended solute particles is used, and dissolved mass of solute is calculated. Results are correlated by the lambda h equation and the (CNIBS)/Redlich-Kister equation. The calculated results of both equations were found to show fine representation of the experimental data.