This study presents a method for the photocatalytic degradation of κ-carrageenan (KC) using UV light, hydrogen peroxide (H₂O₂), and titanium dioxide (TiO₂) to produce carrageenan oligosaccharides (KCO) with low molecular weight. The degradation process was optimized to reduce the average molecular weight of KC to 1.6 kDa within 2 hours. The study compared different degradation methods, including UV, UV/H₂O₂, UV/TiO₂, and H₂O₂/TiO₂, and found that the combined UV/H₂O₂/TiO₂ treatment had the most synergistic effect. Structural characterization using FT-IR, XRD, and SEM showed that the sulfate groups in KC were preserved during degradation, and the molecular structure of KCO remained largely intact. The degradation products were analyzed for chemical composition, and the results indicated that the reducing sugar and uronic acid content increased, while the galactose and total sugar levels decreased. The antioxidant activity of KCO was significantly higher than that of KC, as demonstrated by DPPH and ABTS radical scavenging assays. Additionally, KCO showed enhanced antioxidant activity in vivo, as evidenced by its ability to prolong the lifespan of Caenorhabditis elegans under oxidative stress and UV damage. The study concludes that the UV/H₂O₂/TiO₂ photocatalytic degradation method is an efficient, environmentally friendly, and precise method for producing KCO with controlled molecular weight, which has potential applications in pharmaceuticals, food, and cosmetics.This study presents a method for the photocatalytic degradation of κ-carrageenan (KC) using UV light, hydrogen peroxide (H₂O₂), and titanium dioxide (TiO₂) to produce carrageenan oligosaccharides (KCO) with low molecular weight. The degradation process was optimized to reduce the average molecular weight of KC to 1.6 kDa within 2 hours. The study compared different degradation methods, including UV, UV/H₂O₂, UV/TiO₂, and H₂O₂/TiO₂, and found that the combined UV/H₂O₂/TiO₂ treatment had the most synergistic effect. Structural characterization using FT-IR, XRD, and SEM showed that the sulfate groups in KC were preserved during degradation, and the molecular structure of KCO remained largely intact. The degradation products were analyzed for chemical composition, and the results indicated that the reducing sugar and uronic acid content increased, while the galactose and total sugar levels decreased. The antioxidant activity of KCO was significantly higher than that of KC, as demonstrated by DPPH and ABTS radical scavenging assays. Additionally, KCO showed enhanced antioxidant activity in vivo, as evidenced by its ability to prolong the lifespan of Caenorhabditis elegans under oxidative stress and UV damage. The study concludes that the UV/H₂O₂/TiO₂ photocatalytic degradation method is an efficient, environmentally friendly, and precise method for producing KCO with controlled molecular weight, which has potential applications in pharmaceuticals, food, and cosmetics.