Self-assembled monolayers of two kinds of thiol-derivatized porphyrins, which differ in the number of alkanethiol side chain, have been constructed on Au. X-ray photoelectron, visible and Fourier transform infrared spectra confirmed that surface structure was approximately the same as anticipated; porphyrin molecules having a single chain are somewhat tilted against surface normal, and porphyrins with four chains are oriented coplanar.