A method of producing a resin composition containing an inorganic filler is disclosed, wherein organic cations having a steric hindrance structure are brought into contact with a layered mineral with an equivalent area per unit charge on the layer surface of 40-150 .ANG..sup.2 /charge, then brought into contact with a thermoplastic resin having a solubility parameter of at least 9.5 �cal/cm.sup.3 !.sup.1/2, so as to disperse the layered mineral inside the resin at the molecular level. The resin compositions obtained by this production method have excellent rigidity, heat resistance and impact resistance, and are suitable for use in fields such as, for example, automobiles, household electronic parts, construction materials and industrial materials.