This paper describes some results obtained in an investigation of urea-formaldehyde (UF) resins of different degrees of polymerisation by Matrix-Assisted Laser Desorption/Ionisation Time-of-Flight (MALDITOF) mass spectrometry (MS). MALDI-TOF MS proved to be an appropriate technique for analyzing these types of polymers, bearing in mind that the results of the analysis correspond with previous physical and chemical measurements. This technique enables a relatively swift determination of the degree of polymerisation through the monitoring of key changes in the structure of a polymer. Thus, in the analysis of UF resins, it may be possible to monitor a decrease in the intensity of the monohydroxymethyl urea (MMU) signal, which corresponds to an increase of the mass spectra values in the mass range of higher homologues, above 1000 g/mol. A noticeable difference concerns the signal intensities in the higher mass ranges (up to 1400 g/mol), which corresponds to more branched and longer homologues of the polymers. Especially, a significantly more intensive signal of MMU was registered. The average Mw of the examined samples was between 936 and 1324 g/mol, with a maximal deviation of 20%, depending on the ratios of the reactants.