We have studied the adsorption of HgCl2 on Au surfaces by scanning tunneling microscopy (STM). HgCl2 was found to form a stable, ordered overlayer on Au(111) surface in ambient conditions and it was imaged with molecular resolution. We suggest that the revealed structure is (root 7x root7)R19.1 degrees -2HgCl(2). This model supposes that the HgCl2 molecule bends in the adsorption to have a 123 degrees angle between Cl-Hg bonds. In addition, the adsorption capacity of Au(111) surface for HgCl2 was determined to be 2:7.