Nanometer-scale patterning of thin films was performed by using the atomic force Microscope (AFM) as the exposing tool. The octadecyldimethyl-methoxysilane (ODMS) films were prepared on a silicon (Si) substrate by self-assembled monolayer. Patterning was accomplished through the local degradation of the monolayer as a result of anodic reaction induced by an AFM tip. When the voltage applied to the ODMS monolayer on the silicon substrate, the protruding lines appeared in the exposed regions. After etching probe-scanned substrate, we obtained fine grooves as narrow as 80 nm.