The host-guest energy transfer process in a self-assembled system was investigated by picosecond time-resolved fluorescence spectroscopy. A self-assembled coordination nanocage (Pd6L4) was photoexcited and the appearance of the fluorescence from an encapsulated guest acridine dye molecule was observed. The time constant (1.3 ns) as well as the efficiency (9%) of the energy transfer from the nanocage to the guest molecule was determined.