OBJECTIVE:To determine the oil-water partition coefficients (logP) of rosiglitazone at different pH values by two kinds of methods.METHODS:A shake flask-ultraviolet spectrophotometry method was used to determine plasma concentration of rosiglitazone in water phase and organic phase at variable pH values (0.95,2.0,3.0,4.0,5.07,5.7,6.55,7.06,7.5,8.15,9.21) to calculate logP by using with n-caprylic alcohol-water as simulation system.Above logP values were compared with that calculated by Pallas software.RESULTS:The logP value was lower than 1 when pH value was lower than 4;the logP value was higher than 1 when pH value was ranged from 5 to 9.Measured logP values were in good agreement with that calculated by Pallas software.CONCLUSION:Rosiglitazone exists in the form of hydrochloride salt with good water solubility (pH