In this work the physicochemical characteristics including fatty acids, tocopherols and sterols composition of Ecballium elaterium (L.) A. Rich seed oil was determined. Results showed that linoleic acid (48.64%) and punicic acid (22.38%) were the major polyunsaturated fatty acids. Among the phytosterols, b-sitosterol was the most abundant (396.25 mg/100 g), while the major tocopherol form was c-tocopherol (44.23 mg/100 g). In addition, we evaluated for the first time the effect of E. elaterium seed oil on the growth of human colonic adenocarcinoma (HT29) and fibrosarcoma (HT1080) cell lines. The original finding was its potent antiproliferative effect on both tumour cell lines. This effect was dose-dependent, with half-maximal inhibition values of IC50 = 4.86 lg/ml and 4.16 lg/ml respectively. This pilot study opens the way for further investigation about the potential use of E. elaterium as an anticancer agent.