Enantiomer separation has been often realized with reversed phase liquid chromatography using diastereomerizing reagents with simply-hydrophobized silica. The present study demonstrates that diastereomer selectivity can be enhanced through highly-oriented organic phase produced by achiral poly(octadecyl acrylate)-grafted on silica and a carbonyl-pi interaction due to the acrylate moiety is effective as the driving force for the selectivity enhancement.