Disclosed is an optical isomer separating filler having separating ability/separating characteristics different from those of conventional optical isomer separating fillers, which is capable of separating an optical isomer which cannot be separated by conventional fillers. Specifically disclosed is an optical isomer separating filler wherein a polysaccharide derivative is chemically bonded onto a support. This optical isomer separating filler is characterized in that the halogen content in the filler is 3.0 to 5.0%.