Co-adsorption with molecules that strongly adsorb on metallic surfaces is beneficial in improving the surface-enhanced Raman spectroscopy (SERS) detection sensitivity of some weakly adsorbed molecules or ions. In this paper, the co-adsorption of four deoxyribonucleic acid (DNA) bases: adenine, guanine, cytosine, and thymine with ClO4-, was studied. Factors like adsorption ability, applied potentials, and coexisting anions were examined to illustrate how they affect co-adsorption. We found that the four DNA bases in their protonated forms could co-adsorb with ClO4-. Among them, thymine with the weakest adsorption ability on Au showed the weakest co-adsorption ability with ClO4-. In addition, repulsion from both negative potentials and reduced SERS enhancements of Au substrates at relatively positive potentials led to a decrease in the SERS intensity of ClO4-. Moreover, anions such as Cl-, NO3-, and SO42- were shown to influence the co-adsorption of ClO4- with adenine based on a dynamic and reversible competitive co-adsorption process. The above results are very helpful in optimizing the SERS detection sensitivity of weakly adsorbed ions or molecules via the co-adsorption method. ; National Natural Science Foundation of China [20673086, 20620130427, 20825313]; Natural Science Foundation of Fujian Province, China [2009J05032]