We investigated the effect of allyl thiourea (ATU) on both the electrodeposition and electrodissolution of copper in aqueous sulfuric acid by combining cyclic voltammetry (CV) with electrochemical quartz crystal microbalance (EQCM) studies and surface enhanced Raman spectroscopy (SERS). The results demonstrated that the two-electron transfer reaction is the predominant process for the copper dissolution-deposition process in 1.0 M H2SO4 solution not containing ATU in the potential range -0.65 to 0.05 V versus SCE. In comparison, the copper dissolution-deposition process in 1.0 M H2SO4 solution containing ATU corresponds to a one-electron transfer reaction. The spectral features observed from the SERS studies showed at molecular level that ATU can be adsorbed tilted to the copper electrode surface and that coordination occurs via the sulfur atom. The secondary amino group is nearer to the surface than the primary amino group. SO42- and HSO4- can be coadsorbed on the protonated -NH (CH2CHCH2) groups.