The present invention relates to a solid dispersion comprising cilostazol, and methacrylic acid copolymer S and/or methacrylic acid copolymer L, which is characterized in that cilostazol is retained in an amorphous state in a gastrointestinal tract for a certain period after oral administration.本發明係有關一種包括西洛他唑(cilostazol)與甲基丙烯酸共聚物S及/或甲基丙烯酸共聚物L之固體分散劑,其特徵為西洛他唑於經口投予後於胃腸道中保持不定形狀態一段期間。