We report two-dimensional crystalline structures and motions of mixed thiophene-N-alkylpyrrole oligomers at solid/liquid interfaces as studied by scanning tunneling microscopy(STM). The molecular structure was resolved to obtain the packing structure of the oligomer at the molecular level. The oligomeric molecules show polycrystalline orientations by forming small domains at the solid/liquid interface. The domains were reoriented by continuous STM scans at constant tunneling parameters. Furthermore, the orientation of domains can be reversibly manipulated by changing tunneling parameters. This study shows that STM is a useful technique to understand molecular orientations and domain structures at the molecular level.