A series of vitamin-containing Pt(II) complexes of the type [Pt (FMN) (L)] (FMN=flavin mononucleotide, L=ethylenediamine, 1,3-propanediamine, 1,4-bu-tanediamine) was synthesizd and characterized by IR, electronic absorption, elemental analysis and FAB=Mass. The coordination sites of FMN to Pt(II) ions were determined to be N(5) and O(6) with resultant chelate ring formation. Theses compounds have much better water solubility (30-35 mg/ml) than cisplatin (1 mg/ml). The anticancer activity of this vitamin-containing Pt(II) series was investigated by MTT assay against mouse and human leukemia cell lines in vitro. Among these compounds, FMN (1,4-butanediamine) Pt(II) having seven-membered ring structure as amine ligand showed moderate anticancer activity.