Five oxovanadium(IV) complexes were synthesized using acetyl- and benzoylacetone-S-alkyl-thiosemicarbazones (alkyl=methyl, ethyl, propyl or butyl) and salicylaldehyde. Structural characterization was performed by element analysis, infrared, mass and electronic spectra, and also single crystal X-ray crystallography for one sample. The purity of all the complexes was verified with Miller indices (hkl) observed and calculated angles, 2θ values and crystal sizes obtained from powder XRD diffraction. The in vitro cytotoxic activity was determined for the MCF-7, MDA-MB-231 and 3T3 cell lines with an MTT assay for 72 h. The complexes showed cytotoxicity against MCF-7, MDA-MB-231 and 3T3 cells at concentrations of 73–148, 75–224 and 112–176 μM, respectively. All the complexes had better cytotoxicity than the positive control, fluorouracil (5-FU). The complex containing the S-propyl group was the most effective complex, with the concentrations of 72.9 (for MCF-7) and 75.5 (for MDA-MB-231) µM. Furthermore, the ability of the complexes to inhibit elastase, xanthine oxidase and neuraminidase enzymes and their role in cell death was studied. All the complexes inhibited the elastase and xanthine oxidase enzymes at higher concentrations than the IC50 values found for the cytotoxicity. However, the IC50 values for the inhibition of neuraminidase by the complexes bearing ethyl and propyl groups are better than those of quercetin and are close to the values found for the cytotoxicity.