We have used FTIR with attenuated total reflectance (ATR) technique to analyze the decolourization process of Remazol Blue dye (RB 19) caused by the oxidative activity of lacease enzyme. It is known that laceases catalyze the oxidation of a large range of phenolic compounds and aromatic amines carrying out one-electron oxidations, although also radicals could be formed which undergo subsequent nonenzymatic reactions. The enzyme lacease is a copper-containing polyphenol oxidase (EC 22.214.171.124) which has been tested as a potential alternative in detoxification of environmental pollutants such as dyes present in wastewaters generated for the textile industry. In order to ensure degradation or avoid formation of toxic compounds it is important to establish the mechanism by which lacease oxidizes dyes. In this research individual ATR-FTIR spectra have been recorded for several reaction times between 0 to 236 hours, and the temporal dependence of the reaction was analyzed through the relative diminution of the intensity of the infrared band at 1127 cm -1 (associated to C-N vibration), with respect to the intensity of the band at 1104 cm-1 (associated to S=O) from sulphoxide group. Decolourization process of this dye by lacease could be attributed to its accessibility on the secondary amino group, which is a potential point of attack of laceases, abstracting the hydrogen atom. This decolourization process of remazol blue dye by lacease enzyme might in a future replace the traditionally high chemical, energy and water consuming textile operations. © 2008 American Institute of Physics.