In the search for new, safe, and natural sources as antioxidant and acetylcholinesterase (AChE) inhibitors, eight seaweeds were collected from the intertidal region in KwaZulu-Natal, South Africa and screened. Their total phenolic, flavonoid, and condensed tannin contents were determined, and the specific phenolic acids were identified. The highest total phenolics, flavonoids, and condensed tannin were recorded in Rhodomelopsis africana (7.89 mg gallic acid equivalents g−1), Halimeda cuneata (3.64 mg catechin equivalents g−1), and Codium duthieae (0.60 mg cyanide chloride equivalents g−1), respectively. Based on UHPLC-MS/MS, different concentrations of protocatechuic acid, p-hydroxybenzoic acid, and m-hydroxybenzoic acid were quantified in the seaweeds. The highest radical scavenging ability and oxygen radical absorbance capacity (ORAC) were observed in red Gelidium foliaceum (52.2 %) and green C. duthieae (44 μmol TE g−1), respectively. In terms of AChE inhibition, the green H. cuneata exhibited greatest bioactivity (IC50 = 70 μg mL−1). Overall, the findings suggest that these seaweeds could be potential candidates as new sources of natural antioxidant and AChE inhibitors.