In order to clarify the interactions of alcohol cluster ions such as ethanol and methanol cluster ions with silicon (Si) surfaces, the fundamental properties such as sputtering, irradiation damage and wettability were investigated using the alcohol cluster ion beams. The sputtered depth increased with increase of the acceleration voltage, and the sputtering yield of the Si surfaces at an acceleration voltage of 9 kV was 246 atoms per ion for the ethanol cluster ions and 776 atoms per ion for the methanol cluster ions, which were a few hundreds times larger than that by argon (Ar) ion beam sputtering. Furthermore, the sputtering ratio of Si to SiO₂ by the alcohol cluster ion beams was about 10. This suggests that chemical reactions between Si atoms and alcohol molecules produced silicon hydride even at room temperature, which was the dominant etching material for the Si surfaces. The RBS channeling measurement showed that irradiation damage induced by alcohol cluster ion beams was less than that by Ar monomer ion beams at the same accelerating voltage. In addition, the contact angle measurement showed that hydrophobic and hydrophilic properties of Si surfaces could be controlled by using different kinds of cluster ion beams and adjusting the irradiation conditions. [DOI: 10.1380/ejssnt.2006.473]