Oxidative stress during the periparturient period can impair immune and reproductive functions in cattle. Thus, antioxidant supplements such as selenium (Se) and vitamin E (VE) are increasingly used to support redox balance. However, evidence regarding the effects of combined Se–VE supplementation on gestation length, particularly in beef breeds such as Wagyu, remains limited. This study evaluated supranutritional supplementation with organic Se yeast (Sel-Plex 2000) and VE in pregnant Wagyu heifers (n = 24) fed from approx. 100 days of prepartum to 7 days of postpartum. Treatments included a basal diet (CON), T1 (0.5 mg Se/kg dry matter (DM) + 800 IU VE/kg DM), and T2 (1.0 mg Se/kg DM + 1,600 IU VE/kg DM). Whole-blood Se, serum α-tocopherol, whole-blood glutathione peroxidase (GPx), and erythrocyte superoxide dismutase (SOD) were measured at day 7 and 60 after starting supplementation, and at day 7 of postpartum. Gestation length was the primary reproductive endpoint, while age at first calving, inter-calving period, and service period were also recorded. Compared with CON, both supplemented diets increased whole-blood Se and serum α-tocopherol levels (diet P ≤ 0.014), and elevated GPx activity throughout the trial (diet P ≤ 0.019). A significant diet × day interaction was observed for SOD activity (P < 0.001), indicating a timedependent response to supplementation. Gestation length decreased in a dosedependent manner (least square means 284.25, 276.63, and 270.38 days for CON, T1, and T2, respectively; P < 0.001), whereas other reproductive intervals were not affected (P > 0.05). In conclusion, organic Se–VE supplementation during late-gestation improved systemic antioxidant status and moderately shortened gestation length in Wagyu heifers, supporting its use to improve periparturient redox balance and optimise calving management.