We report the upconversion luminescence of Tm3+ in Y2O2S:Tm, Mg, Ti phosphor. The upconversion luminescence of Y2O2S:Tm, Mg, Ti phosphor and its unusually long-lasting phosphorescence properties have been discussed. Two upconversion emission bands located at 466 and 545 nm from Tm3+ in Y2O2S:Tm, Mg, Ti phosphor are observed after near infrared light (lambda = 798 nm) or red light (lambda = 648 nm) excitation. The afterglow light of Y2O2S:Tm, Mg, Ti phosphor is so strong that it can be seen by the naked eye for above an hour. The possible mechanism of the unusual upconversion long-lasting phosphorescence is also discussed. (C) 2004 The Electrochemical Society.