Alginate, a bioactive polysaccharide fermentable by gut microbiota, has been shown to effectively reduce serum uric acid levels. However, its mechanisms and the role of gut microbiota remain unclear. In this study, we explored the effects of alginate with two different molecular weights on hyperuricemia mice. Both alginates exhibited potent hypouricemic effects through ABCG2 transporter upregulation, effectively ameliorating hyperuricemia-induced renal and intestinal dysfunctions, with the low-molecular-weight alginate demonstrating enhanced bioavailability through microbial biodegradation and superior therapeutic efficacy in hyperuricemia management. Additionally, we found that alginate alleviates gut microbiota dysbiosis induced by hyperuricemia by enriching potentially beneficial bacteria. These include Limosilactobacillus and Lactobacillus, which show a significant negative correlation with serum uric acid levels. These bacteria might regulate uric acid precursors during purine metabolism, thereby reducing uric acid accumulation. In summary, this study reveals the protective effects of alginate on renal and intestinal damage in hyperuricemia mice and highlights the crucial role of gut microbiota. It provides valuable insights into the mechanisms by which gut microbiota mediate the effects of alginate.