A novel water-soluble heptaplatin analogue, cis-[(4R,5R)-4,5-bis-(aminomethyl)-2-isopropyl-1,3-dioxo-lane](3-hydroxy -1,1-cyclobutanedicarboxylato)platinum-(II), has been synthesized and biologically evaluated. The complex shows more activity and less toxicity than its parent drug heptaplatin, exhibiting the great potential for further development.