PROBLEM TO BE SOLVED: To provide an anti-cancer agent that can be used for the treatment of hematologic malignancies and cancer in general, that have similar or greater activity and lower toxicity than arsenic trioxide.SOLUTION: New organic arsenic derivatives, including S-dimethylarsino-glutathione, S-dimethylarsino-thiosuccinic acid and S-dimethylarsino-thiobenzoic acid, are anti-cancer agents which have in-vitro cytotoxic activity against numerous human tumor cell lines, both of solid and hematological origins, as well as against malignant blood cells from patients with leukemia. A method for using the same is also provided.【課題】一般に血液悪性腫瘍および癌の治療に使用することができ、三酸化砒素よりも活性が同等かそれ以上に大きく、毒性が低い砒素誘導体である癌治療剤を提供する。【解決手段】S-ジメチルアルシノ-グルタチオン、S-ジメチルアルシノ-チオコハク酸、およびS-ジメチルアルシノ-チオ安息香酸を含む、新規有機砒素誘導体は固体起源および血液起源の両方の様々なヒト腫瘍細胞株、ならびに白血病患者由来の悪性血液細胞に対する、インビトロ細胞毒性活性を有した癌治療剤及びその使用方法。【選択図】なし