The potential of Eucheuma cottonii (EC) to be a novel source of antioxidants and protection against photoageing is increasingly evident but largely unexplored. This study aimed to evaluate the antioxidant activity and radical scavenging capacity of EC extracts on human keratinocytes. Aqueous and methanol extracts from EC were evaluated in a series of in vitro assays on the HaCaT keratinocyte cell line. Antioxidant activity was determined via the DPPH assay, while MTT was used to evaluate the cytotoxicity of EC extracts up to 72h exposure. Quantitative and qualitative DCFH-DA fluorescence assays assessed intracellular reactive oxygen species (ROS) levels in UVirradiated cells. EC extracts at concentrations from 10 μg/ml were found to possess significant antioxidant activity (p<0.05). Interestingly, the aqueous extract compromised cell viability at high concentrations, while the methanol extract was relatively non-toxic. Intracellular ROS levels significantly decreased with increasing concentration of EC extract treatment (p<0.05). In conclusion, EC extracts demonstrated antioxidant activity and protective effects against UV-induced ROS degeneration in keratinocytes, thus underlining its potential in nutraceutical research to promote skin rejuvenation. 