Equilibrium partitioning of compactin in water-ethyl acetate system was measured at 298 K. The extraction pH showed strong influence on the partitioning ratio: the partitioning ratio decreased with pH. The dissociation constant and distribution coefficients of compactin were determined by treating equilibrium data with numerical approach. Distribution coefficient of compactin in water-ethyl acetate system was treated as a variable and a function of compactin concentration in aqueous solution. The estimated values of dissociation constant and distribution coefficient were compared with the values of water-toluene system. The mutual solubility of ethyl acetate and water was also measured at the same temperature when compactin concentration was varied. The investigation found that increasing compactin concentration increased mutual solubility of water in organic phase as well as of ethyl acetate in aqueous phase. The increasing mutual solubility caused the change of solute composition in aqueous solution and affect equilibrium distribution of compactin. (C) 2003 Elsevier B.V. All rights reserved.