A process for preparing organic smectite applied for thickener, protective colloid, dispersant and binder. The present invention features the process for preparing the organic smectite by mixing smectite incluidng 0 to 20% by weight of interlayer water in the interlayer spaces of said smectite with organic cation-supplying substance selected from at least one of aliphatic alkylamine salts, aromatic amine salts and basic organic compound having pyridine nucleus, and/or basic organic molecule in a mixing ratio of the latter to the former of 10 to 500 milliequivalents per 100 g smectite, and stirring the resulting mixture at a temperature of 5.degree. to 50.degree. C. under an applied pressure of 0.5 to 10 kg/cm.sup.2 to cause a solid-solid reaction. By the process of the present invention, exchangeable organic cations and/or basic organic molecules as a guest substance are intercalated int he interlayer spaces of the smectite as a host substance, thus the hydrophilic smectite can convert to the organic smectite by a more simplified solid-solid reaction than a liquid-liquid reaction.