Sodium deoxycholate in water dissociates into sodium cation and deoxycholate anion in the aqueous phase, and then, the latter anions partially hydrolyze to form deionized deoxycholic acids. The acids move into the benzene phase, when liquid benzene is placed upon the aqueous phase, and finally the partition equilibrium is reached. The above processes were traced by pH change in the aqueous phase by a pH meter or the change in [OH-] with time, from which the rate for transfer of neutralized acid to the organic phase was analyzed. From the trace, the rate constants for hydrolysis of acid anion (k(f)), neutralization of acid (k(b)), transfer of neutralized acid from the aqueous phase to the organic phase (k(in)*), and its back-transfer from the organic phase to the aqueous phase (k(out)*) were evaluated; k(f) = 2.18 x 10(-4) mol(-1) dm(3) min(-1), k(b) = 1.24 x 10(5) mol(-1) dm(3) min(-1), k(in)* = 4.06 x 10(-1) min(-1) cm(-2), and k(out)* = 8.00 x 10(-2) min(-1) cm(-2). The above values are supported by the partition constant of deoxycholic acid between the benzene phase and the aqueous phase.