AbstractFluorescent whitening agents (FWAs) are the most widely used functional chemicals for the manufacture of printing and writing grades of paper. FWAs are used as internal or external additives for the surface treatment on the size press and coater. In spite of the extensive use of FWAs, no method has been established to analyze the FWA content in process water and paper products. Samples are typically exposed to UV light in order to detect the presence of FWAs. This method is based on the fluorescence exhibited by FWAs under a UV-lamp. The observation of fluorescence with the naked eye is highly subjective. Thus, it is essential to develop a more scientific and objective to the quantitative analysis of FWA optical effects. Water and paper samples containing FWAs were prepared in a laboratory. Quantitative analysis was carried out with a spectrofluorometer, a spectrophotometer, and an image restoration microscope. Using these analytical instruments, fluorescence was observed. Regression equations were obtained from the relationship between the fluorescence intensity and the FWA optical effects of the samples.