Fourteen new organotin(IV) complexes with general formula R2SnL2 or R3SnL where R = CH3, C2H5, C4H9, C6H5, C6H11, CH2–C6H5, C(CH3)3, C8H17 and L = N-[(2-methoxyphenyl)]-4-oxo-4-[oxy]butanamide were synthesized and characterized by elemental analyses, FT-IR, NMR (1H, 13C and 119Sn), mass spectrometry and single crystal X-ray structural analysis. Crystallographic data for four triorganotin(IV) complexes (R3SnL, R = CH3, C2H5, C4H9, CH2–C6H5) showed the tin has approximate trigonal bipyramidal geometry with the R groups in the trigonal plane. The carboxylate groups of ligands L bridge adjacent tin atoms, resulting in polymeric chains. In case of the diorganotin(IV) derivatives a six-coordinate geometry at the tin atom is proposed from spectroscopic evidence. The Me–Sn–Me bond angle in complex 7 was determined from the 2J[119Sn–1H] value as 166.3° that falls in the range of six-coordinate geometry. The ligand and its complexes (1–14) were screened for their antimicrobial, antitumor, cytotoxic and antileishmanial activities and found to be biologically active. The ligand and its complexes bind to DNA via intercalative interactions resulting in hypochromism and minor bathochromic shifts as confirmed by UV–visible spectroscopy. Based on in vitro studies such as the potato disc method, the synthesized compounds were found to possess significant antitumor activity. Also, from cytotoxicity and DNA interaction studies, these compounds can also be used for the prevention and treatment of cancer. Gel electrophoresis assay was used to investigate the damage to double stranded super coiled plasmid pBR322 DNA by the synthesized compounds and compounds 1 and 7 were found to cause the maximum damage. All the synthesized compounds exhibit strong antileishmanial activity that was even higher than that of Amphotericin B, with significant cytotoxicity. This study, therefore, demonstrated the potential use of these compounds as source of novel agents for the treatment of leishmaniasis.