Eucheuma cottonii, a widely cultivated seaweed from the Island of Lombok, Indonesia, contains various bioactive compounds. Its utilization, however, is mainly limited based on its high carbohydrate content. Nevertheless, plant fermentation using lactic acid bacteria is renowned for increasing bioactive compounds and enhancing bioactivities. This study unveiled the potential of Lactobacillus plantarum-fermented E. cottonii as a functional food. E. cottonii was fermented using L. plantarum for 24 h. The folin-Ciocalteau method was used to determine the total phenolic content. The antioxidant capacity was measured using a 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assay. Anti-inflammatory activity was carried out using cyclooxygenase (COX) inhibition assay against cervical cancer (HeLa) and colon cancer (WiDr) cells. Overall, fermentation successfully enhanced the bioactivities of E. cottonii. Fermented products exhibited higher antioxidant capacity than unfermented ones. Interestingly, the bioactivities only showed a moderate correlation with total phenolic content. Regarding anti-inflammatory activity, fermented extracts exhibited higher cyclooxygenase inhibition against HeLa cells, whereas no significant differences were observed between the fermented and unfermented products in WiDr cells. These findings indicate that L. plantarum-fermented E. cottonii holds promise to be a profitable functional food and has the potential to be utilized as an additional food therapy for cancer treatment. Keywords: Eucheuma cottonii; fermentation; Lactobacillus plantarum; antioxidant, anti-inflammation.