Thioredoxin (TRX) is a ubiquitous multifunctional thiol protein that is critically involved in maintaining cellular redox homeostasis. Levels of thioredoxin-1 (TRX1), the major isoform of TRX, have been shown to correlate with organismal lifespan and age-associated tissue deterioration. Accordingly, we investigated the direct functional effects of suppressing TRX1 levels on cellular senescence, a phenomenon intimately linked with tissue degeneration and aging. Here we find that suppression of TRX1 expression via shRNA rapidly induces premature senescence in young human skin fibroblasts through upregulation of the p53/p21(Cip1/Waf1) and p16(INK4a) tumor suppressor pathways. Moreover, inhibition of these pathways by introduction of SV40 Large T Antigen prevents TRX1 suppression-induced premature senescence but not susceptibility to oxidative stressors. Thus our results suggest that TRX1 has a role in suppressing senescence in normal cells in addition to its function as a redox-protective protein.