Updated project metadata. Liver are frequently declined for transplantation due to the donor age. It is still unclear how donor age affects the graft quality. Normothermic machine perfusion (NMP) has been proposed as a useful assessment tool prior to transplantation. We aimed to compare the performance of young and elderly rat liver grafts in a small animal NMP model. Grafts from 24 rats were procured, either 3 or 12 months old and perfused for 6 hours at 37°C or stored on ice as a reference group (n=6/group). Livers in both NMP groups cleared lactate and produced bile, with similar pressure, bile production, and pH levels. However, older rat livers showed higher peak transaminase and urea levels. Proteomic analysis revealed differences in protein composition, particularly higher levels of proteins related to oxidoreductase and catalytic activity in older livers. Older age appeared to increase susceptibility to oxidative stress in the livers.