Graphene oxide has been extensively investigated as an electron acceptor due to its exceptional electronic and optical properties. Here we report an unusual ultrafast electron transfer occurring in the nanocomposites of Au nanocluster (Au NC)-graphene oxide (GO) in which GO acts as an electron donor. An ultrafast electron transfer is corroborated from the excited states of graphene oxide into the highest occupied molecular orbital (HOMO) of Au NCs. It is found that the electron transfer rate is significantly higher in Au 10-GO nanocomposites (4.17 × 1012 s-1) than that in Au25-GO (0.49 × 1012 s-1) due to a larger energy difference and smaller sized ligands. This finding suggests that graphene oxide-Au nanocluster nanocomposites can be very useful to construct novel nanostructures with enhanced visible light photovoltaic, photonic and photo-catalytic activities.