Due to its expected low toxicity to human use, more attention is given worldwide to antioxidants of natural sources. Therefore, the extraction of the total phenolic compounds contained in the leaves of Malva sylvestris and the analysis of the polyphenols, flavonoids and tannins contents were carried out. The antioxidant activity of the hydro-methanolic extract of Malva sylvestris was investigated employing various established in vitro systems including 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity, the reduction of hydrogen peroxide and the ferric reducing power assay. The antiproliferative activity of plant extract was tested against three tumor cell lines: MCF-7, Hep2 and WEHI using 3-(4,5-dimethyl thiazol-2-yl)-2,5-diphynyl tetrazolium bromide (MTT) assay. Preliminary screening indicated the presence of substances with large therapeutic values: an important content of polyphenols, flavonoids and tannins was detected in the tested extract. Our data showed that the extract exhibited high antioxidant properties, which were demonstrated by its ability to scavenge 76.11% of DPPH free radicals, and the elimination of 69.97% of hydrogen peroxide at a concentration of 125 µg/ml. In addition, the plant extract showed strong ferric reducing power which was a function of the sample concentration. For the antiproliferative activity, the results demonstrated that the plant extract significantly inhibited tumor cell growth and colony formation in a concentration-dependent manner. The toxicity percentage of extract at 125 µg/ml on MCF-7, Hep2 and WEHI was found in the order of 45.20%, 62.62% and 82.04%, respectively.