Abstract Adlayers of zinc(II) 5,10,15,20-tetraphenyl-21 H,23 H-porphine (ZnTPP) and zinc(II) phthalocyanine (ZnPc) were formed on Au(1 1 1) substrate by immersion in benzene solutions containing these molecules, and they were investigated in 0.1 M HClO 4 by using cyclic voltammetry and in situ scanning tunneling microscopy. Highly ordered epitaxial layers of ZnTPP and ZnPc molecules were obtained by controlling the immersion time. In particular, the epitaxial growth of ZnPc was found to be strongly influenced by the underlying ZnPc adlayer structure. Ordered monolayers of ZnTPP and ZnPc molecules were observed on reconstructed Au(1 1 1) surfaces. At negative electrode potentials, an individual ZnTPP molecule was composed of a set of bright spots in the highly ordered ZnTPP adlayer, showing that a redox reaction proceeded in the framework of TPP. The highly ordered ZnPc adlayers also revealed a structural change induced by the redox reaction in the framework of Pc at negative potentials. Electrochemical potential played a significant role in the redox reactions of ZnTPP or ZnPc molecules on the Au(1 1 1) surface.