The adsorption behaviours of glycine on Cu(111) have been investigated under ultra-high vacuum conditions at room temperature using scanning tunneling microscopy(STM). At lower coverage, it has been found that glycine can form only a two-dimensional gas phase on the Cu(111) surface. When the coverage is high enough, glycine will form a two-dimensional solid phase, i.e., the (4×8) superstructure. Two possible models have been proposed for the (4×8) superstructure. The models can explain STM images well. In addition, in a coverage range between those of the gas and solid phases, two intermediate phases are formed depending on different conditions of deposition and annealing. One is a stripe structure; the other is a hexagonal structure. To understand these intermediate phases further investigations are needed.