A laccase-mediated system for denim overdyeing using phenolic compounds was developed. Laccase from ascomycete Myceliophthora thermophila was able to oxidize phenolic compounds such as catechol and catechin and mediate their attachment to denim surfaces. Laccase-generated polymers gave rise to new coloration states from dark brown to green-yellow and replaced dyes in the overdyeing process. Process parameters, such as enzyme dosage, incubation time and presence of mediator, were studied by considering a compromise between the highest overdyeing level and lower energy/products consumption (2 U/mL laccase; 4 h incubation in the absence of mediator). Enzyme-generated polymers were followed by UV/Vis spectrophotometry and their level of attachment to denim surfaces was evaluated by means of spectral values quantification [k/s, Kubelka-Munk relationship (k=absorption coefficient, s=scattering coefficient)]. Overdyeing of denim with phenolics, such as catechol or catechin, was successfully achieved with acceptable levels in terms of durability. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.