To obtain a resin composition excellent in mechanical characteristics, even when the amount of a lamellar silicate salt is small, and not affecting the appearance of a molded product, when the amount is large, by homogeneously dispersing the lamellar silicate salt in a resin in a state expanding the interlayer distance of the dispersed lamellar silicate salt particles.

This resin composition is obtained by dispersing a lamellar silicate salt (preferably a kaolin group clay mineral such as kaolinite) having a layer electric charge of <0.2 in a resin so as to expand the interlayer distance in comparison with that before the dispersion. The interlayer distances of the dispersed lamellar silicate salt particles are preferably ≥20 angstrom on the average. The lamellar silicate salt is preferably compounded in an amount of 0.1-150 pts.wt. per 100 pts.wt. of the resin. The further addition of a reinforcing agent such as glass fibers in an amount of ≤50 pts.wt. per 100 pts.wt. of the resin is preferable, because the mechanical strength of the resin composition is largely improved without deteriorating the appearance of the resin composition. The objective composition is obtained by preparing a slurry from the lamellar silicate salt and a dispersing medium capable of forming an interlayer compound with the lamellar silicate salt, mixing the slurry with a monomer and/or its low polymerization degree polymer and subsequently finishing the polymerization of the mixture.