Preterm delivery (PTD) is the leading cause of infant mortality and morbidity. However, the mechanism at the molecular level is still unknown. Placental inflammatory response and oxidative stress are associated with PTD. Thioredoxin-1 (TRX-1) regulates oxidative stress, inflammation, and the activities of transcription factors. Objectives: The objective was to detect in placental tissues the expressions of TRX-1 and the TRX-1-related molecules: tumor necrosis factor-alpha (TNF-alpha), cyclooxygenase-2 (COX-2), thioredoxin-1-binding protein-2 (TBP-2), hypoxia inducible transcription factor 1 alpha (HIF-1 alpha), and forkhead box protein O3A (FoxO3A). Methods: PTD was defined as gestation of <37 weeks and term delivery (TD) as >= 37 weeks. The expressions of TRX-1 and TRX-1-related molecules were examined in placental tissues by real-time polymerase chain rection and western blot. Results: The expressions of TRX-1, TNF-alpha, COX-2, HIF-1 alpha, and FoxO3A in the placenta of PTD were significantly higher as compared with TD, but no difference was observed in TBP-2 expression. Discussion: These results indicate that TRX-1 may be adaptively induced by the effects of inflammation and oxidative stress, suggesting protective roles for TRX-1 against these effects in the placenta of PTD.