The aim of this study was to assess the polyphenolic composition and antioxidant capacity of the medicinal plants from the collection of the Scientific Center of Medicinal Plants Cultivation of Nicolae Testemitanu State University of Medicine and Pharmacy: agrimony - Agrimonia eupatoria L. (Rosaceae), chicory - Cichorium intybus L. (Asteraceae.), artichoke - Cynara scolymus L. (Asteraceae) and St John's-wort - Hypericum perforatum L. (Hypericaceae). A qualitative and quantitative characterization of the main phenolic compounds from ethanolic extracts was carried out by HPLC method. The total polyphenolic and flavonoid contents were measured by spectrophotometric methods. The in vitro antioxidant activity of these extracts was evaluated using 2,2-diphenyl-1-picrylhydrazyl (DPPH), Trolox (6-hydroxy-2,5,7,8- tetramethylchroman-2-carboxylic acid) equivalent antioxidant capacity (TEAC), 2,2'-azinobis (3-ethylbenzthiazoline-6-sulphonic acid (ABTS) radical cation scavenging and metal chelating activity. Considering the obtained results, the following order in antioxidant activities was established: A. eupatoria> C. inthybus> H. perforatum> C. scolymus. All species contain significant amounts of polyphenolic compounds and they may be considered an important source of natural antioxidants for pharmaceutical uses.