The fruits of Vaccinium uliginosum L. is rich in anthocyanins and holds significant potential for development, however, systematic research regarding its anthocyanins remains relatively limited. To investigate the antioxidant activities of anthocyanins found in V. uliginosum fruits, the separation, purification, structural identification, and antioxidant activity evaluation of these anthocyanin compounds, as well as the exploration of their structure-activity relationships, were systematically conducted in this study. Seven anthocyanin monomers were obtained and their structures were identified by nuclear magnetic resonance spectroscopy as: cyanidin-3-O-(6-malonylglucoside) (1), cyanidin-3-O-glucoside (2), delphinidin-3-O-rutinoside (3), peonidin-3-O-glucoside (4), pelargonidin-3-O-glucoside (5), delphinidin-3-O-sambubioside (6), and cyanidin-3-O-sambubioside (7). Among these, compounds 1, 3, 5, 6, and 7 were reported from this plant for the first time. The antioxidant evaluation results showed that in the DPPH and ABTS radical scavenging assays, all tested anthocyanins exhibited significantly higher activity than the positive control Vitamin C (Vc). In the reducing power assay, the reducing power of all anthocyanins and Vc increased with concentration, Compound 2 demonstrated the highest reducing power, comparable to that of the highly active Compounds 5 and 7. These results reveals the chemical diversity and antioxidant structure-activity relationships of anthocyanins from V. uliginosum L. fruits, providing a theoretical basis for their development as natural antioxidants and high-value-added products.