Gold nanoparticles (AuNPs) were stably capped with the anti-8-OHdG polyclonal antibody. When 8-OHdG was added, the antibody-capped AuNPs would aggregate for the specific interaction of antibody and antigen. The maximum absorption wavelength of antibody-capped AuNPs red shifts gradually and the solution color changes from red to blue, with increasing concentration of 8-OHdG. Based on that, highly selective determination of 8-OHdG is set up, with a detection range of 0.25–5.00 μg mL⁻¹ and LOD of 25 ng mL⁻¹. The method is simple, rapid and easy to operate. Semi-quantitative determination can also be achieved by visual observation of the solution color change without any apparatus.