The objective of this research was to apply Fourier Transform Infrared Spectroscopy (FTIR) for quantitative determinations of fat and water in mayonnaise. The results of FTIR method were compared with those obtained by reference standard methods in order to verify whether or not they are correct. Low fat, regular and high fat mayonnaise varieties constituted the research material. Spectra of mayonnaise samples in 1–propanol were recorded using a total reflectance (ATR) technique. A FTIR spectrometer involved in this method was equipped with a horizontal zinc selenide (ZnSe) ATR sampling accessory or KRS crystal. On the basis of the spectra obtained, surfaces under two distinct bands: at 1748 cm^-1 and 1650 cm^-1 were calculated. The sections of spectra taken for the calculations corresponded to the vibrations characteristic for the ester group of acylglycerols and the hydroxyl group of water, respectively. Next, using the calibration curves of the standard solutions, those surfaces were converted into contents of relevant mayonnaise components. The determination results of the percentage rate of fat and water using a FTIR method are linearly correlated with those obtained by the reference standard methods. The group of high fat mayonnaises showed the best compatibility of their fat content levels as determined for the purpose of this study. The best agreement in experimental measurements of the fat contents has been received for high fat mayonnaise.