The aim of the work was to study the compounds available in the Deschampsia antarctica plants from various sites on the Argentine Islands region, the maritime Antarctic, as well as to introduce the plants into in vitro culture and to compare the extracts from the plants grown in situ and in vitro. The composition of extracts was investigated using HPLC and MALDI MS methods while antiradical activity was tested in the reactions with DPPH•, NO• and OH• radicals. All the extracts were found to contain high amounts of phenols (up to 900 mg/L), with derivatives of luteolin and hydroxybenzoic acids being the main bioactive compounds in the extracts from the plants grown in situ and in vitro, respectively. All the extracts showed high antiradical activity, under standard tests conditions, 10-fold diluted extracts scavenged 50÷90% of DPPH radicals, 20÷40% of NO• radicals and 40÷60% of OH• radicals. Despite the differences in the composition, extracts from the plants grown in vitro were not inferior as radical scavengers to extracts from the plants grown in situ.