Two classes of dibutyltin(IV) hydroxamates complexes, formulated as the mononuclear mixed-ligand diorganotin(IV) complex [ nBu 2Sn(HL)Cl] a and the tetranuclear [ nBu 4Sn 2(HL) 2(L)] 2 b were fully characterized. X-ray diffraction analyses were also carried out for the representative complexes [ nBu 2Sn(2,6-F 2C 6H 3C( O)NHO)Cl]( 4a) and [[ nBu 4Sn 2{3-BrC 6H 4C( O)NHO} 2{3-BrC 6H 4C( NO)O}] 2]( 1b). The cytotoxicity of all compounds was tested by MTT and SRB assays against three human tumor cell lines HL-60, BGC-823 and KB. 1b and 4a have been shown to be more potent antitumor agents than other compounds and cisplatin. Annexin V FITC-PI assay was consistent with the MTT results. Cell cycle assay results indicated that KB cells displayed an arrest in the G 0/G 1 phase and a decrease of S phase of the cell cycle at the low concentrations of 1b, 4a.