Abstract: The complexation of a dihydroxy bile salt derivative (sodium 3-cetocholate; 3CC), by y-cyclodextrin (?-CD), has been studied by using 1D and 2D-NMR techniques. 3CC forms a 1:1 complex with ?-CD, with a value of (2.24+0.31)×103M-1 for the equilibrium constant. Contrary the complexation of natural bile salts by ?-CD, in which the bile salt enters into the cyclodextrin cavity by its side chain, in the present case, ROESY experiments have clearly stated that the steroid nucleus enters into the cavity by its A ring. It is proposed that this fact is a consequence of the modification of the hydrophobicity of the guest due to the substitution of the 3-hydroxyl group (present in natural bile salts) by the ceto group in 3CC.