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.