Evaluation of the alteration produced by microbiological attack on the poly(vinyl) acetate (PVA) resin Mowilith 50 has been carried out using FTIR spectroscopy and Pyrolysis-Gas Chromatography/Mass Spectrometry (Py-GC/MS). The latter proposed method includes the on-line derivatization of vinyl resins using hexamethyldisilazane during pyrolysis. Specimens consisting of thin films formed on glass slides from drying of an acetone solution of this PVA resin have been used. Analyses performed on the specimens on which different genera of bacteria and fungi were inoculated and allowed to grow, indicate that attack of microorganisms promotes the formation of acidic compounds. IR bands ascribed to carboxylic acids appearing in samples from inoculated specimens as well as an increase in the content of ethanoic acid detected by Py-GC/MS from specimens inoculated with fungi suggest that the effects of metabolic processes in these microorganisms are more significant than those of bacteria.