Colloidal gold nanoparticles having an average diameter of 8 nm were prepared by laser ablation at 1064 nm of a gold metal plate in an aqueous solution of sodium dodecyl sulfate (SDS) and were subjected to fragmentation under irradiation of a pulsed laser at 532 nm. Gold clusters exhibiting no significant optical absorption in the visible wavelength region were produced in a solution, together with nanoparticles. UV-visible optical absorption spectroscopy revealed that the gold clusters grow gradually through attachment to the nanoparticles and through mutual aggregation. The growth processes depend crucially on the concentration of SDS in the aqueous solution of nanoparticles.