The authors have previously reported a method for preparing gold nanoparticles using silver halide photographic materials and gold deposition development. This process was investigated from the viewpoint of the effect of thiocyanate ion concentration. Gold particles are formed on latent image specks on the exposed silver halide grains by the disproportionation reaction of gold(I) thiocyanate complex ions. The ratio A of gold ions to thiocyanate ions in preparing the gold(I) thiocyanate complex affects gold deposition; that is, the rate of gold deposition increases when the abovementioned ratio A increases from 1:10 to 1:3. Optical measurement, atomic absorption spectroscopy, and electron microscopic observation indicate that the growth rate of gold nanoparticles does not depend on the ratio A, while the total mass of gold atoms increases with an increase in the ratio A. The mass increase is due to the increase not in size but in the number of gold particles. Excess thiocyanate ions inhibit the deposition of gold atoms on latent image specks.