Abstract: The ~(13)C and ~1H NMR spectra of antitumor alkaloid platinum complexes such as caffeine, theophylline and theobromine platinum (Ⅱ)complexes were recorded. The ~1H, ~(13)C chemical shifts and carbon-hydrogen coupling constants were obtained for these alkaloids and their platinum complexes. Comparing the variations of δ_H and δ_C in the ligands before and after coordination and combining with the determination of carbon-platinum and hydrogen-platinum coupling constants, we find that the alkaloids coordinate to platinum unidentately, the coordination site is the double bond nitrogen atom on the five membered imidazole ring. The platinum (II) is coordinated with three chloride anions and one alkaloid ligand to form a mononuclear complex anion (PtLCl_3)~-. By heteronuclear proton selected decoupling technique, all the ~1H and ~(13)C NMR spectral lines were assigned.