Abstract: Scanning tunneling microscopy has been developed as a versatile tool capable of visualizing surface adsorbates, performing spectroscopic identification and inducing a variety of chemical and physical processes in situ at single atomic or molecular level. This unique capability allows us to directly reveal novel phenomena that could be hidden in a conventional ensemble-averaged measurement. In this talk, I will introduce some single-molecule experiments carried out in Dr. Wilson Ho's group at UC, Irvine. The research interest has been focused on exploring the intrinsic property-structure correlation of functional organic molecules, such as porphyrin, phthalocyanine and C60. I will discuss the conformation-dependent single molecule electroluminescence; vibronic-state assisted electron transport through single molecule in a double-barrier tunneling junction; electromechanics of ZnEtioI molecule; and an intriguing 2D electron gas behavior we observed in C60 monolayer. Tunneling spectroscopy and optical characterization provide invaluable information about the electronic structure of molecules adsorbed on surface.