Carbon nanodots (CNDs) have emerged as fascinating materials with exceptional electronic and optical properties, and thus they offer many promising applications in photovoltaics and photocatalysis. In this paper we investigate electron transfer in nanocomposites of CNDs-graphene oxide (GO), -multi-walled carbon nanotubes (MWNTs) and -TiO2 nanoparticles without linker molecules, using steady state and time-resolved spectroscopy. Significant fluorescence quenching was observed in the CND-GO system, and it is attributed to the ultrafast electron transfer from CNDs to GO with a time constant of 400 fs. In comparison, carbon nanotubes result in static quenching of fluorescence in CNDs. No charge transfer was observed in both CND-MWNT and CND-TiO2 nanocomposites. This finding suggests that the CND-GO nanocomposite can be an excellent candidate for hot carrier solar cells due to the effective carrier extraction, broad spectral absorption, weak electron-phonon scattering, and thus a slow cooling rate for hot carriers.