A new water-soluble derivative of heptaplatin, cis-{Pt(II)[(4R,5R)-4,5bis(aminomethyl)-2-isopropyl-1,3-dioxolane](3-acetoxyl-cyclobutane-1,1-dicarboxylato)} has been synthesized, characterized by elemental analysis, MS, IR, and 1 H, 13 C NMR, and evaluated for in vitro anticancer activity in four human cancer cell lines. The stability of the derivative in water was also investigated by monitoring the changes of 1 H NMR in D 2 O. The results reveal that the new derivative has good solubility and stability in water and also shows high anticancer activity against gastric cancer cells, ovarian cancer cells, and colon cancer cells. Therefore, it is worthy of further evaluation for in vivo antitumor activity and toxicity.