Adlayers of cobalt(II) and copper(II) phthalocyanines (CoPc and Cupc) prepared on Au(1 1 1) from CoPC- and CuPc-saturated benzene solutions were investigated in 0.1 M HClO4 by using cyclic voltammetry and in situ scanning tunneling microscopy (STM). The CoPe-modified Au(1 1 1) electrode was found to enhance the electrochemical reduction of O-2 to H2O2, whereas the CuPc-modified Au(1 1 1) elect-ode showed no electrocatalytic activity for O-2 reduction. High-resolution STM images revealed the characteristic shape, internal structure, and orientation of each CoPc and CuPc molecule in ordered domains. Both CoPc and CuPc molecules formed three packing arrangements on Au(1 1 1) surface, i.e., one rectangular arrangement on reconstructed Au(1 1 1) and two hexagonal arrangements on Au(1 1 1)-(1 x 1), depending on the surface coverage. The center cobalt ion in CoPc appeared as the brightest spot in the STM image, whereas the copper ion in CuPc appeared as a dark spot.