PURPOSE: To obtain an improved reverse phase filler used for blood serum analysis by bonding a lipophilic distribution phase to the internal surface of a porous support as an internal area.

CONSTITUTION: A porous support having a hydroxyl group, such as porous silica is brought into contact with an unsaturable amount fluorocarbon silane expressed by formula I. Then the support is successively brought into contact with the lipophilic silane expressed by formula II and ketal silane having a porous support. Thereafter, the ends of the hydroxyl group (silanol group) left in both the internal and external areas of the porous support are capped by utilizing end capping treatment performed by arbitrarily using trimethylsill reagent. Finally, a diol group is formed on the porous support by cutting off a ketal atomic group by arbitrarily hydrdlyzing the diol group blocked by produced ketal by using, for example, sulfuric acid.