Objective To address the problem of low bioavailability of polymeric proanthocyanidins (PPCs).Methods PPCs extracted, isolated, and purified from Vitis amurensis seeds were used as the raw materials. The average degree of polymerization (mDP) was used as the evaluation index. Catechin (C) combined with sulfurous acid was employed as the depolymerization reagent. The effects of the catechin-to-PPC mass ratio (m_C∶m_PPC), sulfurous acid amount, reaction time, and temperature on mDP were studied. The depolymerization process was optimized using response surface methodology, and the antioxidant activity of PPC before and after depolymerization was analyzed.Results Catechin combined with sulfurous acid effectively depolymerized PPC from V. amurensis seeds. The optimal depolymerization conditions were as follows: m_C∶m_PPC of 0.45∶1, sulfurous acid addition of 6%, reaction time of 31 min, and reaction temperature of 40 ℃. Under these conditions, the mDP of PPC was reduced to 1.83, 4.09 units lower than before depolymerization. The antioxidant capacity of PPC after depolymerization was significantly improved, with DPPH·, ABTS⁺·, and ·OH radical scavenging abilities being 3.31, 1.28, and 1.21 times higher than those before depolymerization, respectively. The ferricyanide reducing power was also significantly enhanced.Conclusion Catechin combined with sulfurous acid demonstrates effective depolymerization of PPC from V. amurensis seeds, reduces reagent costs, and significantly enhances antioxidant activity.