PURPOSE: To obtain a packing agent having excellent separation capacity and reduced in deterioration suitable for liquid chromatography especially used in optically splitting a ceramic compound, by bonding a specific optically active group to a silica gel through a silane treating agent.

CONSTITUTION: A packing agent for separation represented by formula I (wherein one or more of Y1, Y2 and Y3 is a siloxane part with silica and a silica gel and the remainder thereof is respectively H, 1W20C alkyl, 6W20C aryl, 7W20C arylalkyl, halogen, HO or 1W20C alkoxy, X is an 1W30C spacer, R is an optically active group represented by formula II, A is 2W3C alkylene which may have a substitutend, B is a metal salt of thiocarboxylic acid and * is asymmetric carbon) is used as the packing agent of a liquid chromatography for optically splitting a racemic compound. Especially, by using the packing agent represented by the formula I being a Cu-salt to a metal salt, excellent separation capacity is developed and a required solvent amount is reduced as compared with a conventional one and, therefore, splitting treatment can be performed within a short time.