Tuning of nanostructures of gold nanoparticles (AuNPs) on indium tin oxide (ITO) surfaces could be performed using a seed-mediated growth method. While this method composed of two steps, i.e., a seeding process and a growth process, it was found that the smaller AuNPs with a higher density grew on ITO by adding hexamethylenetetramine (HMT) into a growth solution, which normally contained cetyltrimethylammonium bromide (CTAB) as a capping reagent. The optimal conditions for preparing the denser AuNPs with higher size uniformity were found that the ratio of CTAB:HMT was 1:1. For the electrochemical oxidation of uric acid, the AuNP-attached ITO electrode prepared at the 1:1 ratio of CTAB:HMT had superior electrocatalytic properties to the AuNP-attached ITO electrode prepared with the previous growth solution, i.e., CTAB only. The effects of the nanostructures of AuNPs on the electrocatalytic properties were examined after further tuning, i.e., by repeating the growth treatments. As the result, it was found that an increase in the amount of gold not necessarily improve the electrocatalytic properties, but the smaller and denser attachment prepared with HMT was effective for the case of the oxidation of uric acid. The electrochemical oxidations of ascorbic acid and epinephrine showed the same tendencies. (C) 2010 Elsevier B.V. All rights reserved.