Pancreatic lipase activity toward a series of fatty acid vinyl esters with different chain lengths, solubilized in sodium deoxycholate (NaDC) micelles, was investigated kinetically. The kinetic data could be analyzed on the basis of a fully competitive inhibition mechanism, where substratefree NaDC micelles act as a competitive inhibitor. The values of inhibition constant (K₄), which is the dissociation constant of lipase-NaDC micelle complex, obtained from the reaction of each substrate were in reasonable agreement with one another. On the other hand, the maximum velocity (V) and the Michaelis constant (K_m) increased with decrease in the fatty acid chain length (C₁₄&sime;C₁₂<C₁₀<C₈). The V/K_m values indicate that vinyl dodecanoate and tetradecanoate are better substrates than vinyl decanoate and octanoate in this micellar system. The K_m/K₄ values suggest that the lipase-substrate-solubilizing NaDC micelle complex is less stable than the lipase-substrate-free NaDC micelle complex. The changes in the V and K_m values with chain length were ascribed to the difference in the interaction between the substrate molecule and NaDC micelles.