For many applications, the presence of oxide on Si nanowires (Si NWs) is undesirable because of the difficulty in controlling the SiO2/Si interface properties. Here, we report on the functionalization of 50 nm (in diameter) Si NWs with alkyl chains using a versatile two step chlorination/alkylation process, while preserving the original length and diameter of the NWs. We show that Si NWs terminated with C1-C 10 molecules, through Si-C bonds, connect alkyl molecules to 50-100% of the Si atop sites and provide surface stability that depends on the chain length and molecular coverage. These observation were explained by noting that the longer the alkyl chain the higher the concentration of molecule-free pinholes on the Si NW surfaces and, therefore, the easier the oxidation process. Our results provide evidence that alkyl-Si NWs provide stronger Si-C bonds and higher surface stability in ambient conditions than equivalent two-dimensional (2D) Si surfaces having similar or higher initial coverage. The kinetic mechanism of the alkylation process of Si NW surfaces, the oxidation resistance of the modified structures, and the differences from 2D surfaces are discussed in the article.