Length-defined organic solvent soluble oligo-L-leucines containing an Aib residue were prepared by stepwise elongation and fragment condensation methods, and were used as catalysts in the Julia-Colonna asymmetric epoxidation reaction. The yield and enantioselectivity rose by increasing the number of amino acid units in the catalyst. The enantioselectivity was very sensitive to the reaction solvent. The LR characteristic bands (the amide I region) in CH2Cl2 indicated the soluble catalysts to be of helical structure in solution.