For evaluating the effects of capping reagents on the electron transfer reactions on gold nanoparticles (AuNPs), AuNP-attached indium tin oxide (AuNP/ITO) substrates were fabricated using a seed mediated growth method. In addition to the previous procedures, i.e., the crystal growth of AuNPs on ITO in the presence of cetyltrimethylammonium bromide (CTAB) as a capping reagent in the growth solution, the preparation in the presence of sodium dodecyl sulfate (SDS) was examined to find that the fabrication of AuNP/ITO was also possible with SDS. Systematic measurements of cyclic voltammograms were carried out using the AuNP/ITO electrodes prepared with different surfactants, i.e., cationic CTAB and anionic SDS, for the oxidation of anionic [Fe(CN) 3þ . The results showed that the electrochemical responses were significantly improved on the AuNP/ITO electrodes, not depending on the charges of the capping surfactants and the redox species. Thus, the capping of CTAB and SDS on AuNP/ITO was concluded to be quite weak or less, so that the electron transfer reactions of both [Fe(CN) 6 ] 4À and [Ru(NH 3 ) 6 ] 3þ were not disturbed. The weak or less capping of CTAB and SDS was confirmed by replacing to 3-mercaptopropionic acid. Compared with thiols, the capping with surfactants would be useful in electroanalysis, in particular, of biomolecules, utilizing naked or undisturbed surfaces of AuNPs.