The MnF2:Ce nanocrystals with bright Mn2+ luminescence at room temperature were synthesized via a hydrothermal method using polyethylenimine as surfactant. The Ce3+ → Mn2+ energy-transfer efficiency could reach 65%, and the highest Mn2+ luminescence quantum efficiency was 14% in the MnF2:10%Ce nanocrystals. More interestingly, the Mn2+ luminescence could be reversibly switched on and off by controlling the Ce3+ ↔ Ce4+ redox couples. Our studies may provide new possibilities for improving and regulating the Mn2+ luminescence for fabricating redox switches and biological sensors.