Accelerated oxidation of vanillin was studied by isothermal and non-isothermal differential scanning calorimetry (DSC) in model solutions. Exothermic peaks of DSC thermograms, due to the oxidation of vanillin, were observed. Vanillin oxidation to vanillic acid was confirmed by the detection of vanillic acid in heated vanillin samples using GC–MS. The effect of temperature on vanillin oxidation was studied by conducting DSC experiments with pure vanillin at several different final temperatures and by subsequent determination of vanillin and vanillic acid by GC–MS.Furthermore, the DPPH free radical assay was done on DSC-treated samples as well as on mixtures of vanillin–vanillic acid. The radical-scavenging activity of the samples was increased along with the vanillic acid content. Additionally, the antimicrobial activities and the minimum inhibitory concentrations (MIC) of solutions containing vanillin and vanillic acid against Staphylococcus aureus, Staphylococcus epidermidis, Bacillus cereus, Enterobacter aerogenes, Escherichia coli and Yersinia enterocolitica were determined by the agar well-diffusion method. All tested samples exhibited inhibitory activity against all of the bacteria. Yet, the higher the vanillic acid concentration, the lower was the MIC of the samples. It is concluded that the thermal treatment of vanillin-containing food may lead to products with improved antioxidant and antimicrobial properties.