Gallic acid (GA) has well-known antioxidative, antimutagenic, antiviral and anti-inflammatory properties. GA has been used to label gold nanoparticles for bio-analytical applications, but the effects of gold nanoparticles coated with GA on human cell lines have not been studied. We synthesized GA-coated gold nanoparticles (GA-AuNPs) and compared the biochemical effects of the particles to that of free GA on the human hepatocyte cell line HL-7702. Cell proliferation measurements and apoptosis assays indicated that the presence of GA-AuNPs was less cytotoxic and was less likely to induce apoptosis. Synthesis of the labeled nanoparticles resulted in the oxidation of the two phenolic hydroxyls of GA to their quinine forms. Because this was the only chemical change to the molecule, the differences in toxicity between free GA and GA-AuNPs suggested that these phenolic hydroxyls were necessary for the bioactivity of GA molecules. This study might also reveal a new and easier way to illuminate the importance of the phenolic hydroxyls of GA in the cytocidal and cytopathic effects on cells. (C) 2011 Elsevier Ltd. All rights reserved.