The antioxidant activity of polysaccharides from Garcinia mangostana rind and their derivatives was investigated. Four polysaccharides—UAEE-GMRP, UAEE-GMRP-1A, CM-30, and Ac-30—were evaluated for their ability to scavenge hydroxyl radicals and inhibit lipid peroxidation. The results showed that all four polysaccharides had significant hydroxyl radical scavenging ability, with CM-30 and Ac-30 performing better than the others. CM-30 showed the highest scavenging rate, reaching 72.4% at 2 mg/mL. The scavenging ability was positively correlated with concentration, and chemical modification, particularly carboxymethylation, significantly enhanced the antioxidant activity. CM-30 also exhibited strong lipid peroxidation inhibition, with its inhibitory ability exceeding that of the control group. Carboxymethylation modification was more effective than acetylation in improving water solubility and antioxidant activity. The study concluded that carboxymethylation is a promising method for enhancing the antioxidant properties of polysaccharides. The results indicate that chemical modification can significantly improve the antioxidant activity of polysaccharides, with carboxymethylation being the most effective. The findings suggest that these modified polysaccharides have potential applications in antioxidant applications.The antioxidant activity of polysaccharides from Garcinia mangostana rind and their derivatives was investigated. Four polysaccharides—UAEE-GMRP, UAEE-GMRP-1A, CM-30, and Ac-30—were evaluated for their ability to scavenge hydroxyl radicals and inhibit lipid peroxidation. The results showed that all four polysaccharides had significant hydroxyl radical scavenging ability, with CM-30 and Ac-30 performing better than the others. CM-30 showed the highest scavenging rate, reaching 72.4% at 2 mg/mL. The scavenging ability was positively correlated with concentration, and chemical modification, particularly carboxymethylation, significantly enhanced the antioxidant activity. CM-30 also exhibited strong lipid peroxidation inhibition, with its inhibitory ability exceeding that of the control group. Carboxymethylation modification was more effective than acetylation in improving water solubility and antioxidant activity. The study concluded that carboxymethylation is a promising method for enhancing the antioxidant properties of polysaccharides. The results indicate that chemical modification can significantly improve the antioxidant activity of polysaccharides, with carboxymethylation being the most effective. The findings suggest that these modified polysaccharides have potential applications in antioxidant applications.