In the micellar solution of SDS, the partition coefficient (K x) of following branched alkanols at infinite dilution was determined by applying a differential conductivity method: the alkanols used were i-C m H2 m +1OH (m=4–9, i=1–5) in which the position of OH group (i) shifts from an end to the center of a hydrocarbon chain. The method provides two significant quantities, dα/dX am and dC sf/dC af in addition to K x. The following results have been obtained. (1) The dependence of K x on i indicates that the hydrophobicity of alkanol is weakened with increasing i, whereas the increase in m strengthens the hydrophobicity. (2) The degree of counterion disossiation of micelles (α) is accelerated by the solubilized alkanols in micelles (mole fraction: X am) and the acceleration rate, dα/dX am (=0.17), depends on neither m nor i. (3) In the bulk water, the monomerically dissolved alkanols (concentration: C af) depresses the concentration of free monomer surfactant (C sf), and the depressing rate, dC sf/dC af, in micellar solution is identical with the corresponding quantity, (ΔCMC/ΔC a)o at CMC.