The search for improved cytotoxic agents continues to be an important line in the discovery of modern anticancer drugs. Sarcopoterium spinosum (L.) Spach is mentioned in ethnobotanical surveys as a medicinal plant used for the treatment of cancer. The aim of this study is to investigate and to compare the aerial parts of S. spinosum collected in Italy and Lebanon for their chemical composition and their antiproliferative activity against ACHN, C32, A375, MCF-7, LNCaP and HeLa human cancer cell lines using SRB assay. The main constituent tormentic acid was isolated by MPLC and characterized by spectroscopic techniques (NMR, MS). Non polar compounds were analyzed by GC and GC-MS. S. spinosum showed an interesting antiproliferative activity against ACHN and C32 cell lines with IC50 values of 2.4 and 2.7 μg/ml for S. spinosum from Italy and Lebanon, respectively. Remarkable results were obtained also against A375 and LNCaP cell lines. The cytotoxicity against ACHN cell line could be partially attributed to tormentic acid that demonstrated a higher cytotoxicity than the positive control vinblastine. Close association between the radical scavenging activity (evaluated by DPPH and ABTS assay) and cytotoxicity was also demonstrated. This investigation demonstrated the potential cytotoxic activity of S. spinosum taking into account also that none of the tested extracts, fractions and isolated compound affected the proliferation of normal cell line 142BR. Tormentic acid, the major constituent isolated from S. spinosum, play an important role in the cytotoxicity exhibited by the extract.