Medicinal plants are sources of bioactive compounds with recognized beneficial effects on human health. An example is Osyris quadripartita, also known as Osyris lanceolata, which is known for its traditional therapeutic properties in some African countries. The aim of the present study was to evaluate the antioxidant (free radical scavenging activity, reducing power and lipid peroxidation inhibition), antiinflammatory (inhibition of NO production in lipopolysaccharide-stimulated RAW 264.7 macrophages) and cytotoxic (in a panel of human tumor cell lines and in non-tumor porcine liver primary cells) properties of O. quadripartita, providing a phytochemical characterization of its aqueous extracts and different organic fractions, by using high-performance liquid chromatography coupled to diode array detection and electrospray ionisation mass spectrometry (HPLC-DAD-ESI/MS). Twenty-eight individual phenolic compounds were identified: fifteen flavan-3-ols, six flavones, four flavonols, two phenolic acids and one flavanone derivative. The most abundant compounds in the ethyl acetate fraction were (+)-catechin and procyanidin dimer B1 (EC-4,8-C). Quercetin-3-O-rutinoside was the major compound in both the n-butanol fraction and crude aqueous extract. In most of the samples and assays the antioxidant activity was higher than the one revealed by the positive control gallic acid, with the highest antioxidant activity observed in the ethyl acetate fraction. The same fraction also showed the highest inhibition of NO production and the highest cytotoxicity against MCF-7 and NCI-H460 cell lines. This study highlights the potential of O. quadripartita fractions rich in phenolic compounds to be used in pharmaceutical and cosmetic fields. ; The authors are grateful to the Foundation for Science and Technology (FCT, Portugal) and FEDER under Programe PT2020 for nancial support to CIMO (UID/AGR/00690/2013), LSRE (Project UID/EQU/50020/2013), A. Fernandes (SFRH/BD/76019/2011), R. C. Calhelha (SFRH/BPD/68344/2010) and L. Barros (SFRH/BPD/107855/2015) grants. The authors also thank the University Oran 1, the University Abdelhamid Ibn Badis Mostaganem and the LRZA (Algeria) for nancial support of this research work. ; info:eu-repo/semantics/publishedVersion