Some new organotin(IV) complexes of the general formula, RnSnCl4−n·L [where n = 3, R = CH3 or C6H5; n = 2, R = C6H5; L = Schiff bases derived from the condensation of 2-amino-5-(o-methoxyphenyl)-1,3,4-thiadiazole with salicylaldehyde (L-1), 2-hydroxy-1-naphthaldehyde (L-2), 2′-hydroxyacetophenone (L-3), benzyl methyl ketone (L-4), acetylacetone (L-5), and 2-furancarbaldehyde (L-6)] have been synthesized and characterized by elemental analyses, molar conductances, electronic, infrared, far-infrared, 1H and 119Sn NMR and Mössbauer spectral studies. Thermal studies of three complexes, viz., Ph3SnCl(L-2), Me3SnCl(L-4), and Ph3SnCl(L-5) have been carried out in the temperature range 25—1000 °C using TG, DTG, and DTA techniques. All these complexes decompose gradually with the formation of SnO2 as an end product. In vitro antimicrobial activity of the ligands and their complexes has also been determined against Streptococcus faecalis, Klebsiella pneumoniae, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus Penicillin resistance (2500 units), Candida albicans, Cryptococcus neoformans, Sporotrichum schenckii, Trichophyton mentagrophytes, and Aspergillus fumigatus.