An organophilic-montmollironite (Or-Mon) was prepared by a cation-exchange reaction between sodium-montmollironite (Na-Mon) and dioctadecyldimethylammonium chloride (DODAC). The cation exchange amount of DO-DAC in the Or-Mon was 80 meq/100 g-Na-Mon. This corresponds to the cation exchange capacity (CEC) of Na-Mon. The basal spacing of the Or-Mon was 26.75 A, which could be explained by the formation of a single layer complex with the alkyl chain lying parallel to the silicate surface of Na-Mon.The Or-Mon easily adsorbed a nonionic surfactant (SAA) with an HLB value of about 8. The inclusion ratio of SAA to Or-Mon was 0.2/1.0 in weight, and the inclusion compound (SAA/Or-Mon) had 36.78 A for the basal spacing indicating monolayer adsorption of DODAC into the silicate layer of the Na-Mon interface. SAA/Or-Mon swelled in an oil such as liquid paraffin, resulting in the formation of a gel. The swelling of SAA/Or-Mon may possibly have been induced by entrance of the oil into the interlayer of the SAA/Or-Mon.