With the 2-thienylselenoacetic acid ligand, four new organotin complexes, [Me₃Sn(O₂CCH₂SeC₄H₃S-o)]_n (1), [(Ph₃Sn)₆(O₂CCH₂SeC₄H₃S-o)₆] (2), [(Me₂Sn)₄(μ₃-O)₂(O₂CCH₂SeC₄H₃S-o)₄] (3), and [(PhSn)₆(μ₃-O)₆(O₂CCH₂SeC₄H₃S-o)₆] (4), have been synthesized and characterized by X-ray crystallography, elemental analysis, FT-IR and NMR (¹H, ¹³C, and ¹¹⁹Sn) spectroscopy. The structure analysis indicates that complex 1 adopts a 1D infinite zig-zag chain structure, while complex 2 shows a centrosymmetric hexanuclear 24-membered macrocycle. In contrast, complex 3 and complex 4 display ladder and drum structures, respectively. Examination of the non-covalent intermolecular contacts in complex 3 reveals the existence of the C–H⋯O and C–H⋯π interactions, which play an important function in the supramolecular construction. These compounds are rare examples of selenium carboxylic acid-based organotin derivatives. Furthermore, the anti-tumor activity of complexes 1–3 has also been studied. Importantly, the anti-proliferative properties and possible mechanism of complex 2 are preliminarily investigated. The results demonstrate that complex 2 could induce apoptotic cell death via accumulation of ROS and collapse of the mitochondrial membrane permeabilization (MMP).