Objective: To determine equilibrium solubility of isorhamnetin in water and 1-octanol

then calculate thermodynamic parameters

which might be important for its further studies on formulation development and in vivo absorption. Method: HPLC was established to determine equilibrium solubility of isorhamnetin in water and 1-octanol at different temperatures and its apparent partition coefficient in 1-octanol-water solution system. Result: Solubility of isorhamnetin in water and 1-octanol increased with increasing of temperature.Isorhamnetin was more soluble in 1-octanol than in water.Solubility data of isorhamnetin were fitted with Apelblat classic model

its regression equations in water and 1-octanol were lnxcal=879.18-53895.05/T-126.30lnT (r=0.9997)

lnxcal=-1.32-2699.36/T+0.35lnT (r=0.9998).The dissolution processes in water and 1-octanol over the experimental temperature range were endothermic with increasing of entropy.The apparent oil-water partition coefficient of isorhamnetin at room temperature was 5163(lgP=3.71). Conclusion: Isorhamnetin is a fat soluble compound

its water-solubility is poor.By optimizing preparation process and other methods can improve its oral absorption efficiency and bioavailability.