Using X-ray diffraction and Fourier-transform infrared spectroscopy, we carried out a structure study of vacuum evaporated films and self-assembled monolayers (SAM) of terthiophene. It is shown with vacuum evaporated films that the long axis of terthiophene aligns normal to the surface. On the other hand, terthiophene in the SAM orients parallel to the gold substrate. Our results, which contradict the recent quantum chemical calculations predicting that thiophene would not interact with gold, experimentally demonstrated direct interaction between thiophene and gold.