Two　kinds　of　gold　nanoparticles　with　different　surface-capping　groups　(Au-DT　and　Au-DT-CTAB),　1-dodecanthiol　and　cetyltrimethylammonium　bromide　(CTAB)　are　prepared　by　a　two-phase　method.　Structures　and　linear　optical　properties　of　the　materials　are　characterized　using　transmission　electron　microscopy　and　ultraviolet-visible　absorption　spectroscopy.　The　effects　of　surface　modification　on　nonlinear　optical　(NLO)　performance　and　optical　limiting　behavior　of　gold　nanoparticles　are　investigated　using　the　open　Z-scan　technique　at　a　laser　wavelength　of　532　nm.　The　results　show　that　Au-DT-CTAB　shows　an　enhanced　NLO　effect　in　comparison　with　Au-DT.　The　secondary　modification　with　CTAB　can　not　only　improve　local　field　enhancement　effect　but　also　make　the　contribution　of　thermoelectrons　to　NLO　performance　of　gold　nanoparticles　on　laser　irradiation.　©　2012　Chinese　Physical　Society.