Abstract: The cis-trans isomerization of CH3S-Au-SCH3 driven by the tip of the scanning tunneling microscope is investigated at 77 K. CH3S-Au-SCH3 anchored on the Au(111) surface with the S-Au-S axis parallel to the substrate functions as a molecular switch due to the flipping of the CH3 groups. The bonding between CH3S-Au-SCH3 and Au(111) leads to asymmetric isomerization where one of the two methyl groups flips much more effectively than the other, despite the symmetry of CH3S-Au-SCH3. Our findings suggest the possibility of constructing similar molecular switches that can be operated at room temperature and a potential route for fine-tuning of molecular switches in future nanoscale electro-mechanical devices.