The decay law has been investigated theoretically when electronic excitation energy transfer is efficient. The concept of a nonvanishing closest donor-acceptor distance has been introduced into the theory of Inokuti and Hirayama for energy transfer by exchange interaction. A previous report of Hara and Condo on the same subject based on Inokuti-Hirayama＇s theory has been examined and some mistakes have been found in the theory and experiment. Careful treatment of equations yields a decay law different from that of Hara and Condo. The inclusion of the closest donor-acceptor distance modifies the decay form significantly.