The objective of this experiment was to study changes of antioxidants and antioxidative enzymes in the flooding-stressed sweet potato leaf, as affected by paclobutrazol (PBZ) treatment at 24 h prior to flooding. Sweet potato 'Taoyuan 2' were treated with 0 and 0.5 mg/plant of PBZ, afterwards subjected to non-flooding and flooding-stress conditions for 0, 1, 3, and 5 d, followed by a 2 d drainage period. The study was conducted as a factorial experiment in completely randomized blocks with three replications maintained within a screen house. Plants with various antioxidative systems responded differently to flooding stress according to the duration of the flooding period and subsequent drainage period. The increased levels of antioxidants and antioxidative enzymes observed on different days of flooding afforded the sweet potato leaf with improved flooding tolerance. Glutathione reductase activity in the leaf was significantly enhanced over 5 d continuous flooding followed by a drainage period, in comparison with non-flooding conditions. Under non-flooding conditions, antioxidative system of leaf was regulated and elevated by PBZ pre-treatment. PBZ treatment may enable sweet potato 'Taoyuan 2' to maintain the balance between the formation and the detoxification of activated oxygen species. Our results also show that under flooding-stress conditions, the level of 'Taoyuan 2' antioxidative system is linked to PBZ treatment. Pre-treating with PBZ may increase levels of various components of antioxidative systems after exposure to different durations of flooding and drainage, thus inducing flooding tolerance. PBZ exhibited the important function of enhancing the restoration of leaf oxidative damage under flooding stress after the pre-application of 0.5 mg/plant. These findings may have greater significance for farming in frequently flooded areas.