A stably-dispersed composite of metal nanoparticles and inorganic clay and a method for producing the composite, in which interlayered charges of the clay are replaced with the metal ions, which are then reduced to metal particles by a reducing agent. The metal particles will not aggregate together and can be stably uniformly dispersed with particle sizes smaller than conventional metal nanoparticles, and therefore have better antibiotic effect, catalytic ability and other advantages. Antibacterials in a solvent containing 0.01 wt % or more of the metal nanoparticles and inorganic clay are prepared and confirmed to be effective.