In the present study, nine series of organotin(IV) carboxylates have been synthesized by the reaction of tri-, di- and monoorganotin(IV) chlorides or diorganotin(IV) oxides with carboxylate ligands in dry toluene. The ligands used were N-[(2-methoxyphenyl)]-4-oxo-4-[oxy]butanamide (HL1), N-[(4-methoxyphenyl)]-4-oxo-4-[oxy]butanamide (HL2), N-[(4-methoxy-2- nitrophenyl)] -4-oxo-4-[oxy]butanamide (HL4), (HL3), N-[(2-methoxy-5-nitrophenyl)]-4-oxo-4-[oxy]butanamide N-[(2-methoxyphenyl)]carbamoylbenzoic acid (HL5), N-[(4-methoxy-2- nitrophenyl)]carbamoylbenzoic acid (HL6), N-[(2-methoxy-5-nitrophenyl)]carbamoylbenzoic acid (HL7), N-[(4-methoxy-2-nitrophenyl)]-4-oxo-4-[oxy]butenamide (HL8) and N-[(2- methoxy-5-nitrophenyl)]-4-oxo-4-[oxy]butenamide (HL9). The coordination mode of ligands, structural confirmation and geometry assignment of the complexes both in solid and solution states were made, using different analytical techniques such as FT-IR, multinuclear (1H, 13C and 119 Sn) NMR and X-ray single crystal analysis. Based on these results, the ligands appeared to coordinate the Sn atom through carboxylate moiety. The triorganotin(IV) derivatives mostly demonstrate trigonal bipyramidal geometry both in solid and solution state with few exceptions of tetrahedral geometry. Octahedral geometry was proposed for diorganotin(IV) carboxylates in solution state based on NMR. The interaction of the synthesized compounds with DNA was investigated by UV-visible spectroscopy. A hypochromic effect along with obvious bathochromic shift (red shift) was observed. These are the signs of intercalative mode of interaction. The negative values of ∆G assign the spontaneity of complex-DNA adduct formed. Some of the synthesized complexes were also screened for their antibacterial and antifungal activities against various medically important bacteria and fungi. The triorganotin(IV) derivatives have bactericidal and fungicidal action more than diorganotin(IV) complexes. Most of the compounds were found to have biological activity comparable to the reference drugs and some were found even more active. These observations suggest that these compounds may be used as bactericides and fungicides in future. The antitumor and anticancer activities of the representative compounds present a new line of antitumor agents and could also serve as a potential source of chemoprotective agent(s) which is the major challenge for the chemists at the present time. The synthesized compounds were also screened for the antileishmanial activity and found that some of the compounds exhibit strong antileishmanial activity even higher than that of standard drug, amphotericin B. This study, therefore, demonstrated the potential use of these compounds as a source of novel agents for the treatment of leishmaniasis. One of the representative series was also screened for in vitro urease inhibition activity against Jack bean urease and some of the compounds showed excellent activity of urease inhibition, even more than the standard drug itself. They were tested for their catalytic activity in biodiesel synthesis. They possess high capability of catalyst in the conversion of corn oil into biodiesel. In present work, an environmentally benign process for the production of biodiesel from corn oil using a heterogeneous catalyst was developed and upto 99% conversion of oil into biodiesel was obtained. Thus the synthesized compounds may be used as one of the best choice catalyst in future.