Disclosed is a filler for optical isomer separation which: allows a polymer compound derivative to be immobilized on the surface of a carrier at a high ratio; and is excellent in optical separation ability. The filler is characterized in that the filler is obtained by modifying part of hydroxy or amino groups of a polymer compound having the hydroxy or amino groups with molecules of a compound represented by the following general formula (I) : A-X-Si (Y) n R 3-n , and is carried by a carrier through chemical bonding.