PURPOSE: To provide the above-clay by adding a pillar precursor to clay decreased in cation exchange capacity by fixing to synthesize the interlayer crosslinked clay and subjecting such clay to a hydrothermal treatment to impart cation exchangeability thereto, then adding a pillar precursor thereto.

CONSTITUTION: The base material clay, such as smectite ore, is added to distilled water and the distilled water is stirred to prepare a suspension. The pillar precursors of a cationic oligomer are added to this suspension and thereafter, the suspension is subjected to aging, rinsing, drying, heating and pulverizing to synthesize the interlayer crosslinked clay fixed with the exchangeable cations on the silicate layer of smectite ore, etc. The cations fixed to the silicate layer are desorbed when such interlayer crosslinked clay is subjected to a hydrothermal treatment and eventually the interlayer crosslinked clay having the cation exchangeability is obtd. In succession, the interlayer crosslinked clay having the cation exchangeability is dispersed into the distilled water and the pillar precursors are added again thereto and the interlayer crosslinking is executed by the method similar to the above-mentioned method, by which the pillar quantity is increased and the interlayer crosslinked clay having the higher pillar distribution density is obtd.