Reaction of nanocrystalline ("porous") silicon with phenyllithium and lithium phenylacetylide results in functionalization of the silicon surface with phenyl and phenylacetylene moieties? respectively. The reaction proceeds by addition of the aryllithium reagent across a surface Si-Si bond, resulting in a Si-aryl bond and Si-Li species. The highly reactive Si-Li surface species is readily hydrolyzed by water, resulting in significant surface oxidation. The surface-bound Li can also be replaced with H or acyl species by addition of trifluoroacetic acid? acetyl chloride, heptanoyl chloride, or 4-butylbenzoyl chloride. These latter treatments significantly reduce the rate of air oxidation of the porous silicon surface. The nanocrystalline silicon samples used display visible photoluminescence arising from quantum confinement effects. Functionalization with phenyllithium preserves some of the photoluminescence. while the lithium phenylacetylide reaction results in almost complete loss of photoluminescence from the silicon nanocrystallites.