Abstract: AIMThe interactions between diorganotin (IV) complexes of 1,3-dimethyl-4-acetyl-5-pyrazolone (HL₁) and mono-nucleotides together with DNA near physiological condition were investigated. METHODSThe mode of action of the diorganotin (IV) complexes with mononucleotides and DNA under different conditions and different times were investigated by high resolution NMR technology and UV spectra. RESULTSThe interaction of ［(L₁)₂SnEt₂］ with AMP was shown to result in significant change of chemical shift of H(8), H(2) and ³¹P of AMP. Hyperchromic effect of DNA could be observed due to the interaction of; ［(L₁)₂SnEt₂］ with DNA, while interaction of ［(L₁)₂SnMe₂］ with AMP and DNA could only cause obvious change of chemical shift of ³¹P and lead to hypochromic effect of DNA. CONCLUSIONThe results indicate that ［(L₁)₂SnEt₂］ can selectively bind to the N₁ atom of the base and the phosphate oxygen atom of AMP and may further destroy the helical structure of DNA, while the dimethyltin(IV) compound of 1,3-dimethyl-4-acetyl-5-pyrazolone ［(L₁)₂SnMe₂］ merely binds to the the phosphate oxygen atom of AMP and causes the contraction of DNA helical structure.