The exchange interaction is considered to play the dominant role in the quenching of 5D0—7F2 emission of Eu3+ in Y2O3 nanocrystals.Luminescence decay curves of 5D0-7F2 of Eu3+ in two sizes of nanocrystals were measured.We fit the luminescence decay curve by the Inokuti-Hirayama theory.The efficiencies of energy transfer of exchange interaction were calculated.The difference between theoretical and experimental curves of efficiency was analyzed.