PURPOSE: To obtain a filler which can be used for reverse phase chromatography or dimension exclusive chromatography by mixing a porous support having a diol group blocked by ketal on its surface in the filler.

CONSTITUTION: A porous support having a hydroxyl group such as porous silica is brought into contact with the ketal silane expressed by formula II. After contact, the hydroxyl group (silanol group) left on both the internal and external surfaces of the support is treated for end cap by arbitrarily using a reagent, such as the trimethylsilyl reagent which caps ends. Consequently, a filler which can be used for reverse phase liquid chromatography is obtained. The filler has a diol (KBD) group blocked by ketal on both the internal and external surfaces of the porous support. The diol group is formed on the surface of the support by cutting off the ketal group by hydrolyzing the ketal group. Therefore, a dense diol bonded phase can be obtained.