The treatment with venom from scorpion Rhopalurus junceus has raised great interest in the last years, due to the popular knowledge that it cure some illness, included the cancer. The main goal of this study was to determine the cytotoxic effect of scorpion venom and fractions against the human tumor cell lines Hela, (human cervix carcinoma); Hep-2, (human larynx carcinoma); NCI-H292, (lung carcinoma) and normal cell line MRC-5, (human lung fibroblast). The effect of scorpion venom and fractions on cell lines was determined by a colorimetric assay using the (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and the 50% cytotoxic concentration was calculated by linear regression analysis. The scorpion venom was fractionated by liquid chromatography with a molecular exclusion column. The mechanism of cellular death was studied. The venom and their fractions with low molecular below 4 kDa significantly inhibited the growth of tumor cells and the normal cells showed lesser sensibility. The venom caused the cellular death through the apoptosis in tumor cells. The proteins of low molecular weight present in venom of Rhopalurus junceus are the responsible for the significant and differential toxicity against tumor cell.