To obtain a composite material having excellent mechanical properties by melt-mixing a polyamide resin with a layered silicate, an acid having a specified pKa value, an organic substance having a group convertible into an onium ion and water in a specified ratio.

This material is obtained by mixing 100 pts.wt. polyamide resin such as nylon 6 having an average molecular weight of 3,000-70,000 with 0.3-40 pts.wt. layered silicate such as swellable fluoromica, 0.01-5 mol equivalents, per equivalent of the cation exchange capacity of the layered silicate, of an acid (e.g. formic acid) having a pKa of 0-6, 0.3-20 mol equivalents, per equivalent of the cation exchange capacity of the layered silicate, of an organic substance (e.g. 12-aminododecanoic acid) having a group convertible into an onium ion and 50-800 pts.wt., per 100 pts.wt layered silicate, water. The layered silicate used is water-swellable, contains alkali and alkaline earth metal ions among the layers, has a side length of a layer of 10-1,000 nm on the average, has a cation exchange capacity of 20-300 milliequivalents/100 g and is dispersed in the polyamide resin on a molecular level.