Scanning tunneling microscopy (STM) has been used to study the adsorption of aspartic acid on the Cu(001) surface at room temperature.At lower coverage,there ex ist two different bonding states and the corresponding diffusion activation ener gies are 079±001eV and 088±005eV,respectively.When the coverage is inc reased,the aspartic acid molecules can finally form an overlayer with uniform co ntrast but could never form any ordered structures.It has been also found that t he adsorption of aspartic acid cannot make steps faceted.It is interesting that all these features are quite different from the adsorption behaviors of other am ino acids on Cu(001),such as glycine,alanine,phenylalanine and lysine,which do n ot have the β-caboxylate.