Di-2,4-dichlorobenzyltin-2-(2-(thiophen-2-formyl)hydrazono)-propanoic carboxylate complex I {[C₄H₃S(O)C=N-N=C(CH₃)COO]₂[(2,4-Cl₂-C₆H₃CH₂)₂Sn]₂(CH₃OH)₂} and di-2,4-dichlorobenzyltin-2-(2-(thio- phen-2-formyl)hydrazono)-3-phenylpropanoic carboxylate complex II {[C₄H₃S(O)C=N-N=C(PhCH₂)COO](2,4- Cl₂-C₆H₃CH₂)₂Sn}_n were synthesized and characterized by IR, ¹H, ¹³C and ¹¹⁹Sn NMR spectra, HRMS, elemental analysis and thermal stability analysis, and the crystal structures were determined by X-ray diffraction. The crystal of complex I belongs to monoclinic system, space group P2₁/n with a = 11.987(3), b = 35.359(9), c = 12.982(3) Å, b = 103.028(5)°, Z = 4, V = 5361(2) ų, D_c = 1. 688 Mg·m^–3, m(MoKα) = 1.463 mm^–1, F(000) = 2704, R = 0.0572 and wR = 0.1423. The crystal of complex II is of monoclinic system, space group P2₁/n with a = 15.5758(17), b = 9.6020(10), c = 19.599(2) Å, b = 98.886(2)°, Z = 4, V = 2896.0(5) ų, D_c = 1.663 Mg·m^–3, m(MoKα) = 1.357 mm^–1, F(000) = 1440, R = 0.0341 and wR = 0.0936. In vitro antitumor activities of both complexes were evaluated by MTT against three human cancer cell lines (MCF7, NCI-H460 and HepG2), and they all exhibited good antitumor activity. The interaction between complexes and calf thymus DNA was studied by UV-vis and fluorescence spectroscopy, it indicated intercalation as probable mode of interaction.