The bioactivity (antioxidant and cytotoxic activities) of the aqueous and methanolic extracts of Arenaria montana L., a plant commonly used in Portuguese folk medicine, was evaluated and compared.Furthermore, the phytochemical composition was determined based on hydrophilic (sugars, organic acids and phenolic compounds) and lipophilic (fatty acids and tocopherols) compounds, in order to valorize this plant material as a functional food/nutraceutical. Fructose, oxalic acid, methyl-luteolin 2 00 -O-feruloylhexosyl-C-hexoside, a-tocopherol, and linoleic acid were the main individual compounds found in A. montana. In general, the aqueous extract showed higher antioxidant and cytotoxic activities than the methanolic extract; the latter showed activity only against HeLa and HepG2 cell lines. Both aqueous and methanolic extracts showed some hepatotoxicity but at higher doses than the ones active for tumor cell lines. Moreover, the aqueous extract of A. montana may be used as a functional food or nutraceutical due to the high antioxidant and cytotoxic activities, and due to the presence of bioactive compounds. As far as we know, this is the first report on the phytochemical composition and bioactivity of A. montana.