Using carboxyl functionalized porphyrin and plthalocyanine as building blocks and alkane derivatives as coadsorbates, two-dimensional hydrogen-bonded networks were formed on graphite surface and observed by scanning tunneling microscopy. The configuration of the hydrogen bonding in the 2-D structure of 5,10,15,20-tetrakis (4-carboxylphenyl)-21H,23H-porphyrin (TCPP) is found to be different from that in the 3-D structure in bulk crystal. The difference of these structures from that expected from the bulk crystal is attributed to the effect of minimization of surface free energy in the 2-D system, which leads to close packing symmetry of molecules on the substrate.