Resuscitation with fresh frozen plasma (FFP) is associated with improved outcomes after hemorrhagic shock. Many trauma centers are using thawed plasma that has been stored for up to 5 days at 4°C (refrigeration), yet the effect of refrigeration on FFP is relatively unknown. Previously, our group showed that refrigeration of FFP changed its coagulation factors and diminished its beneficial effects on endothelial cell (EC) function and resuscitation in an animal model of hemorrhagic shock. We hypothesize that growth factor composition of FFP is altered during refrigeration, leading to a diminished beneficial effect on EC. Transforming growth factor (TGF-β) is a potent inhibitor of EC migration and is released during refrigeration of platelets. We found increased TGF-β1 protein levels and greater activation of downstream mediators Smad2/3 during refrigeration of FFP. Both day 0 FFP (used on the same day after being thawed) and day 5 FFP (used after being thawed and refrigerated for 5 days) stimulated EC migration in vitro; however, the EC migration in day 5 FFP was significantly reduced. Inhibition of TGF-β type I receptor blocked FFP-induced Smad3 signaling in EC cells and restored the effectiveness of day 5 FFP on EC migration to a comparable level seen in day 0 FFP. These data suggest that the increased TGF-β levels during FFP refrigeration contribute to the deterioration of refrigerated FFP's effects on EC migration. This study identifies a novel molecular mechanism contributing to the reduced efficacy of refrigerated FFP.