Blood is a precious commodity, with storage limited to 42days under refrigeration. Degradative changes in red blood cells (RBCs) begin as early as 11-21days after collection, and compromise their function. Materials that extend the life of RBCs will improve blood utilization in the field, as well as in hospital settings. Cerium oxide nanoparticles (CeONPs) are widely used in the materials industry to counteract oxidative stress and improve oxygen storage. We have previously shown that CeONPs extended the lifespan of cells in culture and counteract oxidative stress in vitro and in vivo. Here, we test the hypothesis that CeONPs extend the lifespan of RBCs in whole stored blood. Rat whole blood was collected with sodium citrate and stored at 4°C. Groups consisted of control (no CeONPs), and 10 and 100nM CeONPs (average particle size 10nm) added. Aliquots of stored blood were removed weekly and analyzed for different blood parameters. Results demonstrate that CeONPs improve storage and functional lifespan of RBCs in stored whole blood. This work suggests that CeONPs may be a promising additive for extending storage and function of blood and blood products.