Chiral modifiers have gained much attention because they can induce high enantioselectivity on reactive metal surface in heterogeneous enantioselective catalysis. The high enantioselectivity is attributed to that the chirality of modifiers is bestowed onto the metal surface upon adsorption. Much study on the adsorption of modifiers on metal surface has been performed in an ultrahigh vacuum. In this paper, the adsorption of tartaric acid on Cu(111) has been studied by electrochemical scanning tunneling microscopy (STM) in aqueous solution. It is found that (R,R)-tartaric acid and (S,S)-tartaric acid can form a well-ordered adlayer on the Cu(111) surface with a (4 x 4) symmetry. A dimeric structure is proposed in the temporary model from STM observation.