The adsorption of three amino acids, L-valine (Val), L-leucine (Leu), and L-phenylalanine (Phe), bearing different substituted groups was investigated on a Cu(111) electrode by in situ electrochemical scanning tunneling microscopy (ECSTM). All three molecules are found to form well-ordered adlayers on the surface. Two stable adlayers of L-Val with the symmetry of (3 x 3) and (2 x root3) were found at the investigated potential range, while L-Leu and L-Phe form similar (4 x 4) adlayer structures. With high-resolution STM images, the internal structural information of adlayers was obtained and the structural models for the three adlayers were proposed.